Intelligent data compression

ABSTRACT

Determining whether to compress data of a virtual storage unit based at least in part on: an I/O activity value of a virtual storage unit; a compressibility value of the virtual storage unit; and/or a capacity utilization of the storage system or a component thereof. For example, decision logic may be configured based on one or more of such parameters such that virtual storage units with relatively high I/O activities are rarely or never compressed, e.g., to avoid the disproportionately high increases in CPU and bandwidth resource consumption and I/O latency this could create. Decision logic may be configured such that, in general, the likelihood that a virtual storage unit will be compressed increases as: the I/O activity of the virtual storage unit decreases; the system capacity utilization increases; and/or as the compressibility value of the virtual storage unit increases.

BACKGROUND

In modern computer systems, vast amounts of data may need to be accessed by hundreds, thousands or even millions of different entities, including persons and of persons groups (e.g., organizations). Accordingly, computer systems have been developed in which data is stored on multiple physical storage devices (“PSDs”) including, but not limited to magnetic tape, disk drives, solid state storage devices (SSDs, e.g., flash drives) or portions thereof. Typically, these PSDs are grouped together as part of one or more data storage systems (e.g., storage arrays), for example, data storage systems made available by EMC Corporation, headquartered in Hopkinton, Mass. (“EMC”).

Entities typically access the data on such data storage systems via one or more host systems (i.e., “hosts”) for which communication paths have been established over one or more communication media (e.g., as part of a network) between ports of the host systems and ports of the data storage systems. Through the host systems, data of the data storage system may be accessed and modified using I/O operations, for example, read and write operations. To this end, data storage systems may provide storage services to host systems (e.g., servers). Host systems typically do not address the PSDs of the storage system directly, but rather, access the PSDs by addressing virtual (i.e., logical) storage units (VSUs) such as, for example, logical devices, logical volumes (LVs), thin devices and storage groups, which hide the details of actual physical storage from the host.

To save storage space on a data storage system, data to be written to a non-volatile medium of the storage system disk may be compressed before being stored so the data takes up less storage space. However, compressing the data, and decompressing it in response to a read I/O operation consumes system resources, including CPU cycles and internal bandwidth, and also can increase I/O latency.

SUMMARY

This Summary provides an illustrative context for aspects of the invention, in a simplified form. It is not intended to be used to determine the scope of the claimed subject matter. Aspects of the invention are described more fully below in the Detailed Description.

In some embodiments, a system comprising one or more physical data storage media and a plurality of virtual storage units is provided, in which each VSU is associated with one or more physical address ranges of the one or more physical storage media. For first data associated with a first of the plurality of VSUs, it is determined whether to compress the first data based at least in part on an I/O activity value (e.g., rate or frequency) of the first VSU. If it is determined to compress the first data, the first data is compressed.

In some aspects of such embodiments, determining whether to compress the first data is based at least in part on a compressibility value of the first VSU.

In some aspects of such embodiments, it is determined whether to update a compressibility value of the first VSU. If it is determined to update a compressibility value of the first VSU, the compressibility value of the first VSU is updated.

In yet other aspects of such embodiments, determining whether to compress the first data is based at least in part on a storage capacity utilization of the storage media or a subcomponent thereof.

In some aspects of such embodiments, determining whether to compress the first data is performed in response to receiving a write I/O request for the first data.

In some aspects of such embodiments, prior to determining whether to compress the first data, an initial write I/O request for the first VSU, specifying to write second data to a first one or more physical address ranges associated with the first VSU, is received; and a compressibility value of the first VSU based on the compressibility of the second data is determined, irrespective of a storage capacity utilization of the storage media or a subcomponent thereof.

In yet other aspects of such embodiments, it is determined that a compressibility value has not been determined for the first data for at least a threshold amount of time. In response to such determination, a compressibility value for the first data is determined.

In some embodiments of the invention, a system is configured with logic to perform one or more of the foregoing acts. Such logic may be embodied in one or more discrete modules of the system.

In some embodiments of the invention, a computer-readable storage device is provided, encoded with computer-executable instructions that, as a result of being executed by a computer, control the computer to perform one or more of the foregoing acts.

Other advantages, novel features, and objects of the invention, and aspects and embodiments thereof, will become apparent from the following detailed description of the invention, including aspects and embodiments thereof, when considered in conjunction with the accompanying drawings, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment or aspect of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating an example of a data storage system, in accordance with some embodiments of the invention;

FIG. 2 is a block diagram illustrating an example of logical internal communications between directors and memory of a data storage system, in accordance with some embodiments of the invention;

FIG. 3 is a block diagram illustrating an example of components that may be included in a service processor, in accordance with some embodiments of the invention;

FIGS. 4, 5A and 5B are examples illustrating a data storage system, such as data storage array, including a plurality of storage tiers in an embodiment in accordance with techniques herein;

FIG. 5C is a schematic diagram illustrating tables that are used to keep track of device information in connection with an embodiment of the system described herein;

FIG. 5D is a schematic diagram showing a group element of a thin device table in connection with an embodiment of the system described herein;

FIGS. 6 and 7 are examples illustrating a storage group, allocation policy and associated storage tiers in an embodiment in accordance with techniques herein;

FIGS. 8A and 8B are examples illustrating thin devices and associated structures that may be used in an embodiment in accordance with techniques herein;

FIG. 9 is an example illustrating data portions comprising a thin device's logical address range;

FIG. 10 is an example of performance information that may be determined in connection with thin devices in an embodiment in accordance with techniques herein;

FIG. 11 is a graphical illustration of long-term and short-term statistics described herein;

FIG. 12 is a flowchart of processing steps that may be performed in an embodiment in accordance with techniques herein; and

FIG. 13 is an example of a graph representing levels of compressibility and I/O activity value in accordance with some embodiments of the invention;

FIG. 14 is a flowchart illustrating an example of a method of intelligently compressing virtual storage unit data in accordance with some embodiments of the invention;

FIG. 15 illustrates an example of a data structure for compression decision data in accordance with some embodiments of the invention; and

FIG. 16 is a flowchart illustrating an example of a method of determining whether to compress data of a virtual storage unit in accordance with some embodiments of the invention.

DETAILED DESCRIPTION

A typical storage system exhibits I/O workload skew, in which a relatively small physical address range of the system (e.g., represented by a VSU) is subject to a disproportionately high share of the I/O operations. For example, 85% of I/O operations may correspond to 15% of physical address space, or even 5-10% of the physical address space in a highly skewed environment. Conversely, a relatively large physical address range may be subject to a disproportionately low share of the I/O operations. This skew can be utilized to make dynamic determinations over time of which data to compress within a storage system, while achieving an acceptable balance between capacity utilization on the one hand, and compute and bandwidth resource consumption and I/O latency on the other hand.

Described herein are mechanisms and techniques for determining whether to compress data of a VSU based at least in part on: an I/O activity value (e.g., rate or value) of a VSU; a compressibility value of the VSU; and/or a capacity utilization of the storage system or a component thereof (collectively “compression decision parameters”). For example, decision logic may be configured based on one or more of such parameters such that VSUs with relatively high I/O activities are rarely or never compressed, e.g., to avoid the disproportionately high increases in CPU and bandwidth resource consumption and I/O latency this could create. Conversely, decision logic may be configured based on one or more of such parameters such that VSUs with relatively low I/O activities are always or almost always compressed. Decision logic may be configured such that, in general, the likelihood that VSU data will be compressed increases as: the I/O activity value of the VSU decreases; the system capacity utilization increases; and/or as the compressibility value of the VSU increases. Decision logic may be implemented in software, firmware or hardware, or any suitable combination thereof. Capacity utilization of a storage system or component thereof is a measure of a relative amount (e.g., percentage) of storage capacity of storage system or component thereof, respectively, currently being used. As used herein, “system capacity utilization” means the capacity utilization of a storage system or component thereof.

A “VSU” may be a software abstraction representing any of the following: storage group, a logical device, a thin device, a logical volume; an extent, a sub-extent, a track, a sector, a block, another type of storage object, or any suitable combination of the foregoing. A VSU may or may not correspond one-to-one to a PSD or a sub-component thereof. It may be desirable to select a type of VSU to which to apply the techniques and mechanisms described herein at a logical level of granularity that achieves a suitable balance between degree of control and flexibility on the one hand, and consumption of compute, bandwidth and storage resources on the other. In some embodiments, it may be desirable to have VSUs be at the sub-logical volume level, e.g., be extents and/or sub-extents to achieve such balance.

In some embodiments, Fully Automated Storage Tiering (FAST) technology made available from EMC may be employed, which is described in more detail below, may be used to collect, calculate and store compressibility data and values. The logical level at which the compressibility or I/O activity data may be collected (e.g., in accordance with FAST techniques) may be at a lower logical level than the level of the VSU for which a compressibility value or I/O activity value is being determined, and the collected data may be aggregated into a tally for the higher level VSU. For example, even though the VSU for which compressibility and/or I/O activity value is determined may be an extent or sub-extent, data may be collected at the sub-extent, chunk or even lower level, respectively, and the counts for these lower levels aggregated together for a next higher level, and the totals for the next higher level may be tallied together for a yet higher level, etc. For example, if an I/O count is being tallied for an extent, the total I/O operation counts for each chunk belonging to the extent may be counted and the counts from such chunks may be tallied for their respective sub-extents to produce sub-extent totals; and the sub-extent totals may be tallied for their respective extents to produce extent totals.

Similarly, in addition to counts being tallied at lower levels, compressibility values or I/O activity values themselves may be determined at lower logical storage levels than the level of the VSU for which the compressibility value or I/O activity value ultimately is being determined, and the compressibility values or I/O activity values, respectively, of such sub-levels may be suitably combined to produce the compressibility value or I/O activity value, respectively, of the VSU. Conversely, the compressibility values or I/O activity values may be determined at higher logical levels than the level of the VSU for which the compressibility values or I/O activity values ultimately are being determined, and the compressibility value or I/O activity value used for the VSU in determining whether to compress the VSU may be that of the higher level VSU of which the VSU is a member. For example, compressibility value and/or I/O activity value may be determined at the extent, logical volume or storage group level, and may be used as the compressibility value and/or I/O activity value for the constituent sub-extent, extent and logical volume members, respectively to determine whether to compress their data.

The logical levels at which adding count totals stops and combining compressibility values or I/O activity values begins may be configured, taking into account many factors, including, the computation cost of counting and/or combining values, the desired granularity of visibility, and the desired granularity of action (e.g., compression).

In some embodiments, the compressibility value for a VSU may be calculated at least in part based on a compression ratio of one or more data that are written to the VSU over time. A compressibility ratio of data X may be defined as: (uncompressed size of X):(compressed size of X), e.g., 3:1 (i.e., 3), where the compressed size of X is determined by application of a compression function. Any suitable compression function may be used, but should be used consistently across VSUs over time.

In some embodiments, a plurality of levels (e.g., high, moderate, low) for each of one or more of the compression decision parameters may be defined, each level corresponding to a range of values for the respective parameter, and decisions about whether to compress data may be determined based on the levels of one or more of these parameters. Further, in some embodiments, the history of compressibility values is considered (e.g., by accessing in a data structure) in determining a compressibility level, and the compressibility level may be determined based at least in part on such history. For example, if there is a large degree of volatility historically in the compressibility value determined for a VSU, a compressibility level may be assigned that is greater than the level associated with the determined compressibility value, as is described below in more detail.

In some embodiments, a decision is made whether to compress the data within a VSU each time a write I/O request is received. Decision logic may be configured such that, if a write I/O request is an initial write I/O request for a VSU, i.e., a new allocation—a first-ever write to a physical storage address range represented by the VSU, then the write I/O data may be compressed, and an initial compressibility value determined for the VSU. In some embodiments, compression decisions are made as part of a process that is executed: periodically; in response to user input; in response to a detected change in change in compression decision parameter level; and/or in response to another system event. Such a process is often referred to herein as “compression scanning process.” The compression scanning process may determine whether to compress any VSUs that are uncompressed at the time the process is run. For example, a VSU may have been previously uncompressed because, at the time of a most recent write I/O operation, the system capacity utilization was low; but at the time the process is executed, the system capacity utilization value may be high, such that the decision logic determines that the VSU should now be compressed. It should be appreciated that, as used herein, “compressing a VSU” and the like means to compress the data represented by the VSU.

In some embodiments, compression scanning logic may be configured to scan, and potentially compress, uncompressed VSUs in a predefined order, for example, based on the I/O activity value and/or compressibility value of the VSUs. For example, one or more indexes and/or ordered lists of uncompressed VSUs may be created in accordance with such logic, and traversed by the compression scanning logic as part of performing compression scanning.

The techniques and mechanisms described herein may be used with any type of data storage, including any of those described herein, including SSDs (e.g. flash) and HDDs described in more detail below.

EXAMPLES

Referring to FIG. 1, shown is an example of an embodiment of a system that may be used in connection with performing the techniques described herein. The system 10 includes a data storage system 12 connected to host systems 14 a-14 n through network 18 including one or more communication media. In this embodiment of the computer system 10, the n hosts 14 a-14 n may access the data storage system 12, for example, in performing input/output (I/O) operations or data requests. The network 18 may include any of one or more of a variety of networks or other type of communication connections as known to those skilled in the art. The network 18 may include any of: a network connection, bus, and/or other type of data link, such as a hard wire or other connections known in the art. For example, the network 18 may include any of: the Internet, an intranet, a network (including a Storage Area Network (SAN)), a network-attached storage network (NAS) and other wireless or other hardwired connection(s) by which the host systems 14 a-14 n may access and communicate with the data storage system 12, and also may communicate with other components included in the system 10.

Each of the host systems 14 a-14 n and the data storage system 12 included in the system 10 may be connected to the network 18 by any one of a variety of connections as may be provided and supported in accordance with the type of network 18. The processors included in the host systems 14 a-14 n may be any one of a variety of proprietary or commercially available single or multi-processor system, such as an Intel-based processor, or other type of commercially available processor able to support traffic in accordance with each particular embodiment and application.

It should be noted that the particular examples of the hardware and software that may be included in the data storage system 12 are described herein in more detail, and may vary with each particular embodiment. Each of the host systems 14 a-14 n and data storage system 12 may all be located at the same physical site, or, alternatively, also may be located in different physical locations. Each such site may be its own data center or any two or more sites may be considered a distributed data center. The one or more communication media of network 18 that may be used to provide the different types of connections between the host computer systems and the data storage system of the system 10 may use a variety of different communication protocols such as SCSI, Fibre Channel, Fibre Channel-over-Ethernet, iSCSI, and the like. Some or all of the connections by which the hosts and data storage system may be connected to the one or more communication media may pass through other communication devices, such as, for example, switching equipment including, but not limited to, a phone line, a repeater, a multiplexer or even a satellite. For example, while not shown in FIG. 1, system 10 may include a switch connected between host system 14 and data storage system 12 such as, for example, a Connectrix® switch made available from EMC.

Each of the host computer systems may perform different types of data operations in accordance with different types of tasks. In the embodiment of FIG. 1, any one of the host systems 14 a-14 n may issue a data request to the data storage system 12 to perform a data operation. For example, an application executing on one of the host systems 14 a-14 n may perform a read or write operation resulting in one or more data requests to the data storage system 12.

It should be noted that although element 12 is illustrated as a single data storage system, such as a single data storage array, element 12 also may represent, for example, multiple data storage arrays alone, or in combination with, other PSDs, systems, appliances, and/or components having suitable connectivity, such as in a SAN, in an embodiment using the techniques herein.

It should also be noted that an embodiment may include data storage arrays or other components from one or more vendors. In subsequent examples illustrating the techniques herein, reference may be made to a single data storage array by a vendor, such as by EMC Corporation of Hopkinton, Mass. However, as will be appreciated by those skilled in the art, the techniques herein are applicable for use with other data storage arrays by other vendors and with components other than those described herein for purposes of example.

The data storage system 12 may be a data storage array including a plurality of PSDs 16 a-16 n. The PSDs 16 a-16 n may include one or more types of PSDs such as, for example, one or more disk drives and/or one or more solid state drives (SSDs). An SSD is a PSD that uses solid-state memory to store persistent data. An SSD using SRAM or DRAM, rather than flash memory, also may be referred to as a RAM drive. SSD may refer to solid state electronics devices as distinguished from electromechanical devices, such as hard drives, having moving parts. Flash devices or flash memory-based SSDs are one type of SSD that contains no moving parts. As described in more detail in following paragraphs, the techniques herein may be used in embodiments in which one or more of the PSDs 16 a-16 n is a flash drive. More generally, the techniques herein also may be used with any type of SSD although the following paragraphs may make reference to a particular type such as a flash device or flash memory device.

The data storage array also may include different types of adapters or directors, such as one or more HA(s) 21 (host adapter), RA(s) 40 (remote adapter), and/or PSD interface(s) 23. In a VMAX or VMAX3 storage system, such an adapter and director may be implemented and/or referred to as “emulation.” The term “HA” is used herein interchangeably with the term “FA,” and the term “PSD interface” is used herein interchangeably with the term “BE.” Each of the adapters may be implemented using hardware including a processor with local memory with code stored thereon for execution in connection with performing different operations. The HAs may be used to manage communications and data operations between one or more host systems and the global memory (GM). In an embodiment, the HA may be, or include, a Fibre Channel Adapter or other adapter which facilitates host communication. The HA 21 may be characterized as a front-end component of the data storage system which receives a request from the host. The data storage array may include one or more RAs that may be used, for example, to facilitate communications between data storage arrays, including data storage arrays located outside of proprietary computer network 62 to which the data storage array belongs, as will be described below in more detail. The data storage array also may include one or more PSD interfaces 23 for facilitating data transfers to/from the PSDs 16 a-16 n. The data storage interfaces 23 may include PSD interface modules, for example, one or more disk adapters (DAs) (e.g., disk controllers), adapters used to interface with SSDs, e.g., flash devices, and the like. The DAs and SSD interfaces also may be characterized as back-end components of the data storage system which interface with the PSDs.

One or more internal logical communication paths may exist between PSD interfaces 23, RAs 40, HAs 21, and memory 26. An embodiment, for example, may use one or more internal busses and/or communication modules. For example, the global memory portion 25 b may be used to facilitate data transfers and other communications between the PSD interfaces, HAs and/or RAs in a data storage array. In one embodiment, the PSD interfaces 23 may perform data operations using a cache that may be included in the global memory 25 b, for example, when communicating with other PSD interfaces and other components of the data storage array. The other portion 25 a is that portion of memory that may be used in connection with other designations that may vary in accordance with each embodiment.

The particular data storage system as described in this embodiment, or a particular PSD thereof, such as a disk or particular aspects of an SSD, should not be construed as a limitation. Other types of commercially available data storage systems, as well as processors and hardware controlling access to these particular PSDs, also may be included in an embodiment.

Host systems provide data and access control information through channels to the data storage systems, and the data storage systems also may provide data to the host systems through the channels. The host systems do not address the PSDs 16 a-16 n of the data storage systems directly, but rather access to data may be provided to one or more host systems from what the host systems view as a plurality of VSUs, e.g., logical devices or logical volumes (LVs). The LVs may or may not correspond to the actual PSDs. For example, one or more LVs may reside on a single PSD or multiple PSDs. Data in a single data storage system, such as a single data storage array, may be accessed by multiple hosts allowing the hosts to share the data residing therein. The HAs may be used in connection with communications between a data storage array and a host system. The RAs may be used in facilitating communications between two data storage arrays. The DAs may be one type of PSD interface used in connection with facilitating data transfers to/from the associated disk drive(s) and LV(s) residing thereon. An SSD interface may be another type of PSD interface used in connection with facilitating data transfers to/from the associated SSDs and LV(s) residing thereon. It should be noted that an embodiment may use the same or a different PSD interface for one or more different types of PSDs than as described herein.

The PSD interface, such as a DA, performs I/O operations on a PSD 16 a-16 n. In the following description, data residing on an LV may be accessed by the PSD interface following a data request in connection with I/O operations that other directors originate. Data may be accessed by LV in which a single PSD interface manages data requests in connection with the different one or more LVs that may reside on a PSD 16 a-16 n. For example, a PSD interface may be a DA that accomplishes the foregoing by creating job records for the different LVs associated with a particular PSD. These different job records may be associated with the different LVs in a data structure stored and managed by each PSD interface.

Also shown in FIG. 1 is a service processor 22 that may be used to provide data (e.g., I/O) services and/or storage management services for system 12. In one embodiment, the service processor 22 may be used in collecting performance data, for example, regarding the I/O performance in connection with data storage system 12. This performance data may relate to, for example, performance measurements in connection with a data request as may be made from the different host systems 14 a-14 n. This performance data may be gathered and stored in a storage area. Additional detail regarding the service processor 22 is described in following paragraphs.

It should be noted that a service processor 22 may be peripheral to the data storage system 12 and may communicate with the data storage system 12 using any one of a variety of communication connections. In one embodiment, the service processor 22 may communicate with the data storage system 12 through three different connections: a serial port, a parallel port and using a network interface card, for example, with an Ethernet connection. Using the Ethernet connection, for example, a service processor may communicate directly with DAs and HAs within the data storage system 12.

In some embodiments, as an alternative, or in addition, to service provider 22, storage system 12 may include a data services component 24 and/or a storage management component 28. Storage management component 28 may provide any of a variety or storage management services, for example, one or more storage management tools and applications, including one or more user interfaces, APIs, CLIs or any suitable combination of the foregoing. For example, in some embodiments of the invention, storage system 12 may be, be included within, or include a VMAX3 system made available from EMC, and storage management component 28 may be, be included within, or include a Management Module and Control Station (MMCS) made available as part of a VMAX3 system. Storage management component 28 may be used to configure one or more data service parameters of other components of storage system 12 including, but not limited to, HA 21, RA 40, PSD interfaces 23 and data services component 24, for example, to implement one of more aspects of the invention described herein.

Data services component 24 may provide any of a variety of data services, for example, any of those described herein in relation to service processor 22, including, but limited to FAST services (described below) and/or other data services described in relation to performance data monitoring software 134 and optimizer 138. For example, in embodiments of the invention in which storage system 12 is, is included within, or includes a VMAX3 system, data services storage management component 28 may be, be included within, or include one or more Enginuity™ Data Services modules (EDSs) made available as part of a VMAX3 system (such modules also are referred to sometimes as “emulations”). It should be appreciated that one or more other elements (e.g., one or more PSD interfaces 23, HAs 21 and/or RAs 40 data services) may be configured to implement one or more data services, or portions thereof, described herein as being performed by data services component 24.

In some embodiments, to enable one or more data services and/or storage management functions to be executed internally within storage system 12, storage system 12 may include an embedded storage hypervisor (not shown), which enables these data services and management functions to be run on their own threads, so as to not interfere with other (e.g., core or traditional) storage activities running within the storage system 12. For example, in embodiments of the invention in which storage system 12 is, is included within, or includes a VMAX3 system, a HyperMax™ hypervisor from EMC may be provided.

Referring to FIG. 2, shown is a representation of the logical internal communications between the directors and memory included in a data storage system. Included in FIG. 2 is a plurality of directors 37 a-37 n coupled to the memory 26. Each of the directors 37 a-37 n represents one of the HAs, RAs, or PSD interfaces that may be included in a data storage system. In an embodiment disclosed herein, there may be up to sixteen directors coupled to the memory 26. Other embodiments may allow a maximum number of directors other than sixteen as just described and the maximum number may vary with each embodiment.

The representation of FIG. 2 also includes an optional communication module (CM) 38 that provides an alternative communication path between the directors 37 a-37 n. Each of the directors 37 a-37 n may be coupled to the CM 38 so that any one of the directors 37 a-37 n may send a message and/or data to any other one of the directors 37 a-37 n without needing to go through the memory 26. The CM 38 may be implemented using conventional MUX/router technology where a sending one of the directors 37 a-37 n provides an appropriate address to cause a message and/or data to be received by an intended receiving one of the directors 37 a-37 n. In addition, a sending one of the directors 37 a-37 n may be able to broadcast a message to all of the other directors 37 a-37 n at the same time.

With reference back to FIG. 1, components of the data storage system may communicate using GM 25 b. For example, in connection with a write operation, an embodiment may first store the data in cache included in a portion of GM 25 b, mark the cache slot including the write operation data as write pending (WP), and then later de-stage the WP data from cache to one of the PSDs 16 a-16 n. In connection with returning data to a host from one of the PSDs as part of a read operation, the data may be copied from the PSD by the appropriate PSD interface, such as a DA servicing the PSD. The PSD interface may copy the data read into a cache slot included in GM which is, in turn, communicated to the appropriate HA in communication with the host.

As described above, the data storage system 12 may be a data storage array including a plurality of PSDs 16 a-16 n in which one or more of the PSDs 16 a-16 n is a flash memory device employing one or more different flash memory technologies. In one embodiment, the data storage system 12 may be a Symmetrix® DMX™ or VMAX® data storage array by EMC Corporation of Hopkinton, Mass. In the foregoing data storage array, the PSDs 16 a-16 n may include a combination of disk devices and flash devices in which the flash devices may appear as disk drives to the various software tools used in connection with the data storage array. The flash devices may be constructed using nonvolatile semiconductor NAND flash memory. The flash devices may include one or more SLC (single level cell) devices and/or MLC (multi-level cell) devices.

It should be noted that the techniques herein may be used in connection with flash devices comprising what may be characterized as enterprise-grade or enterprise-class flash drives (EFDs) with an expected lifetime (e.g., as measured in an amount of actual elapsed time such as a number of years, months, and/or days) based on a number of guaranteed write cycles, or program cycles, and a rate or frequency at which the writes are performed. Thus, a flash device may be expected to have a usage measured in calendar or wall clock elapsed time based on the amount of time it takes to perform the number of guaranteed write cycles. The techniques herein also may be used with other flash devices, more generally referred to as non-enterprise class flash devices, which, when performing writes at a same rate as for enterprise class drives, may have a lower expected lifetime based on a lower number of guaranteed write cycles.

The techniques herein may be generally used in connection with any type of flash device, or more generally, any SSD technology. The flash device may be, for example, a flash device which is a NAND gate flash device, NOR gate flash device, flash device that uses SLC or MLC technology, and the like, as known in the art. In one embodiment, the one or more flash devices may include MLC flash memory devices although an embodiment may utilize MLC, alone or in combination with, other types of flash memory devices or other suitable memory and data storage technologies. More generally, the techniques herein may be used in connection with other SSD technologies although particular flash memory technologies may be described herein for purposes of illustration.

As noted above, one or more RAs 40 may be configured to facilitate communications between data storage system 12 and other data storage systems, including without limitation any of a variety of data storage system available from EMC, such as, for example, storage systems from the VMAX, VNX®, VNXe®, XtremIO™ and Isilon® product families, and data storage systems made available from other vendors such as, for example, IBM, HP, Hitachi Data Systems (HDS) and NetApp. In some embodiments, data storage system 12, including one or more RAs 40, may be configured to incorporate one or more of such other data storage systems into a tiered storage strategy (e.g., FAST), for example, using Federated Storage Tiering (FTS) technology made available by EMC, e.g., as described on the date of filing at http://www.emc.com/collateral/hardware/white-papers/h10698-federated-tiered-storage-wp.pdf, the contents of which are hereby incorporated by reference in their entirety.

Data storage system 12 may be part of a proprietary computer network 62, in which access to the network resources are under the purview or control of a single entity (via ownership or a contractual relationship—e.g., a lease), including without limitation a person or organization, for example, a business entity, government agency, education institution, other type of organization or any suitable combination of the foregoing. Network 62 may include any of hosts 14 a, 14 b, 14 n, service processor 22, data storage system 12, cloud gateway 64, elements of network 18 described herein and other resources. Network 18 may include one or more network elements that define a firewall 63 for network 62, which restricts access to resources of network 62. Firewall 63 may be considered to define a virtual boundary between proprietary computer network 62, and resources that are external to network 62, for example, cloud-based storage systems 70 a-n.

System 10 may include multiple cloud-based storage systems 70 a-n that each provide cloud-based storage 72 a-n, respectively, and are not part of proprietary computer network 62, but rather are under the purview of a different entity than the entity that controls network 62. Such systems 70 a-n may include multiple data centers, and may be geographically diverse. For example, one or more of system 70-c may be provided by cloud storage providers, for example, Amazon Web Services, Inc. (AWS), Google and Apple, Inc. to name a few. Cloud storage providers typically store data according to object-based storage protocols. While storage resources within network 62 may exchange I/O communications with each other using standardized data storage protocols and interfaces (e.g., APIs), including without limitation SAN- and NAS-based protocols such as SCSI, iSCSI, Fibre Channel, Fibre Channel-over-Ethernet, NFS (Network File System), SMB (Server Message Block), CIFS (Common Internet File System) and AFP (Apple Filing Protocol), cloud storage providers typically are configured to utilize different, often non-standardized, provider-specific, cloud-based storage protocols and interfaces (e.g., APIs) for I/O communications. Such cloud storage protocols and interfaces include without limitation those of AWS, Dropbox, OpenStack, Google and Apple, and are often based on, or utilize, underlying object-based and/or Internet-based storage protocols and interfaces, such as, for example, HTTP (hyper-text transport protocol), JSON (JavaScript Object Notation) and SOAP (Simple Object Access Protocol), among others. It should be appreciated that network 62 also may include cloud-based storage systems (not shown) that are under the purview or control of the same entity that controls network 62.

In some embodiments (e.g., when implementing FTS), one or more of the other storage arrays with which an RA 40 facilitates I/O communications may be a storage system located outside of (i.e., “external” to) network 62, and which may be a cloud-based storage system, for example, any of systems 70 a-n. As used herein, an “external storage system” is a storage system located outside of a proprietary network. In some such embodiments, FAST.X™ technology available from EMC may be employed, and in aspects of this embodiment, a tiered storage strategy (e.g., FAST) may be employed. The response times for I/O requests from hosts 14 a-n to data stored within data storage system 12 (e.g., on one of PSDs 16 a-c) may be faster than those for data accessed from other data storage systems remotely connected to data storage system, especially if the other data systems is not the same type as data system 12 and/or employs different storage technology and/or if the other data storage system is external to the proprietary network 62. However, it may be cheaper to store data on such other data storage systems. For this reason, in a tiered storage scheme, the lower tiers (e.g. the lowest tier) in which less important and/or less frequently accessed data (e.g., archived data or backup data), i.e., “cold” data, is stored may be implemented using remote storage systems, including external and/or cloud-based storage systems (e.g., 70 a-n). In such a tiered storage scheme, host systems may remain unaware of the precise locations and PSUs on which their data is stored, including that their data is stored externally and/or on a cloud-based storage system.

As noted above, I/O communications between network resources within network 62 may be in accordance with one or more standard SAN- or NAS-based storage protocols or interfaces, and I/O communications with cloud-based storage systems, whether internal or external (e.g., any of systems 70 a-n) to network 62, may be in accordance with one or more cloud-based storage protocols or interfaces. To facilitate I/O communications between data storage system 12 and cloud-based storage systems, one or more RAs may be configured to translate between NAS- and SAN-based protocols and interfaces, on the one hand, and cloud-based storage protocols and interfaces on the other. For example, one or more RAs 40 may be configured with cloud storage gateway technology, for example, as described in U.S. patent application Ser. No. 14/619,627, titled “Cloud-to-Cloud Data Migration Via Cache,” by Anthony et al. filed on Feb. 11, 2015, and/or cloud gateway technology found within an EMC CloudArray® system. For example, RA 40 may implement a virtual version of EMC CloudArray. Other cloud storage gateway technologies may be employed.

For example, an I/O read request or write request may be issued from one of hosts 14 a-n using a SAN- or NAS-based protocol that employs SCSI commands (i.e., a SCSI-based protocol) and received on communication path 51 by an HA 21. Such communication may be processed using one or more components of data storage system 12, including without limitation memory 26, storage management component 28, data services component 24, and RA 40. One of these components may determine that the I/O request corresponds to data stored on a cloud-based storage system (e.g., one of systems 70 a-n), and RA 40 may translate the I/O request into an I/O request conforming to one or more cloud-based storage protocols associated with the destination cloud-based storage system, and transmit such cloud-based I/O request via communication path 61 and network 18 to the destination cloud-based storage system. The cloud-based storage system may respond to the cloud-based I/O request with a cloud-based I/O response in accordance with one or more cloud-based storage protocols. RA 40 may receive the cloud-based I/O response, translate it into a SAN- or NAS-based I/O response, and initiate transmission of the SAN- or NAS-based I/O response through data storage system 12, via HA 21 to the requesting host 14.

In some embodiments of the invention, a cloud storage gateway 64 may be provided, which is a separate component from data storage system 12, and which includes some or all of the translation functionality described above in relation to RA 40. Gateway 64 may be an EMC CloudArray appliance, and may include a cache 65. The data of an I/O write request bound for a cloud-based storage system initially may be stored in cache 65, before being de-staged to the cloud-based storage system. In embodiments of the invention in which cloud storage gateway technology is embodied in RA 40, data storage system 12 or RA 40 itself may have a cache dedicated to cloud-base storage systems, and/or use one or more portions of memory 26. One or more RAs 40 and a cloud storage gateway 64 may be configured to collectively perform any of the cloud gateway techniques described herein, e.g., translation between SAN- and NAS-based interfaces and protocols and cloud storage-based protocols.

In some embodiments in which an I/O operation is performed remotely (i.e., the I/O operation of an I/O request received at storage system 12 is performed on another storage system—i.e., the remote storage system), synchronous storage techniques may be employed, in which a response indicative of completion, failure or otherwise of the I/O request is sent to the host only after an indication of completion, failure or otherwise is received from the remote storage system. In some embodiments in which an I/O operation is performed remotely, asynchronous storage techniques may be employed, in which a response indicative of completion or failure of the I/O request may be sent to the host before an indication of completion or failure is received from the remote storage system. In such embodiments, one or more RAs may be configured to implement such asynchronous storage techniques. Such techniques may include, in the case of a write operation to a cloud-based storage system and/or a storage system external to the proprietary network of the host, sending an indication of completion or failure to the host in response to the write operation being cached in a local cache (e.g., 65 or 25 b) before being de-staged to the cloud-based and/or external storage system. One or more RAs 40 and/or cloud storage gateway 64 may be configured to implement the synchronous and asynchronous techniques described herein.

Illustrative embodiments of the invention, which may be implemented using any suitable system or component thereof of the systems described in relation to FIGS. 1-3, will now be described.

Embodiments in accordance with techniques herein may have one or more defined storage tiers. For example, in some embodiments, FAST technology made available from EMC may be employed, which provides for the optimization of the use of different storage tiers including the ability to easily create and apply tiering policies (e.g., allocation policies, data movement policies including promotion and demotion thresholds, and the like) to transparently automate the control, placement, and movement of data within a data storage system based on business needs. In some embodiments, the FAST techniques described in the following patent may be employed: U.S. Pat. No. 8,838,931, issued Sep. 16, 2014, “Techniques for automated discovery and performing storage optimizations on a component external to a data storage system” to Marshak, et al., which is hereby incorporated by reference in its entirety.

Each tier may generally include PSDs having one or more attributes associated with a definition for that tier. For example, one embodiment may provide a tier definition based on a set of one or more attributes. The attributes may include any one or more of a storage type or storage technology, a type of data protection, device performance characteristic(s), storage capacity, and the like. The storage type or technology may specify whether a PSD is an SSD drive (such as a flash drive), a particular type of SSD drive (such using flash or a form of RAM), a type of magnetic disk or other non-SSD drive, a rotational speed of the drive (e.g., 7.2K RPM, 10K RPM, 15K RPM), and/or the interface type of the PSD (e.g., Fibre Channel (FC), SATA (Serial Advanced Technology Attachment) or SAS (Serial-attached SCSI)), and the like. Data protection may specify a type or level of data storage protection such, for example, as a particular RAID level (e.g., RAID1, RAID-5 3+1, RAIDS 7+1, and the like). Performance characteristics may relate to different performance aspects of the PSDs of a particular type or technology, for example, rotational speed of a disk drive (e.g., 7.2K, 10K or 15K). Storage capacity may specify the amount of data (e.g., in bytes) that may be stored on a PSD. An embodiment may allow a user to define one or more such storage tiers. For example, an embodiment in accordance with techniques herein may define two storage tiers including a first tier of all SSD drives and a second tier of all non-SSD drives. As another example, an embodiment in accordance with techniques herein may define three storage tiers including a first tier of all SSD drives which are flash drives, a second tier of all disk drives of a relatively high rotational speed or range of speed (e.g., 10K, 15K, 10-15K or greater than 7.2K), and a third tier of all disk drives having a relatively low rotational speed or range of speed (e.g., 7.2K, less than 10K, or 7.2K or less). A disk drive having a relatively high rotational speed (e.g., 10K or 15K) may be referred to herein as a “high-speed disk drive” and a disk drive having a relative low rotational speed (e.g., 7.2K RPM) may be referred to herein as a “low-speed disk drive.” The foregoing are some examples of tier definitions and other tier definitions may be specified in accordance with techniques herein.

Referring to FIG. 3, shown is an example 100 of software that may be included in a service processor such as 22. It should be noted that the service processor may include any one of a variety of commercially available processors, such as an Intel-based processor, and the like. Although what is described herein shows details of software that may reside in the service processor 22, all or portions of the illustrated components also may reside elsewhere such as, for example, on any of the host systems 14 a-14 n. For example, all or portions of optimizer 138 and/or performance data monitoring software 134 may be implemented as part of data services component 24, and all or portions of storage management component 135 may be implemented as part of storage management component 28 of storage system 12. Service processor 22 may include a storage management component 135 that enables performance of one or more storage management functions, such as, for example, provisioning storage. Service management component may include one or more user interfaces, APIs and CLIs that enable such management, and may utilize performance data 136 to help do so. It should be appreciated that, although storage management component 135, performance data monitoring software 134 and optimizer 133 are illustrated as discrete components in FIG. 3, the invention is not so limited, as any of various combinations of the three elements is possible.

Included in the service processor 22 is performance data monitoring software 134 which gathers performance data about the data storage system 12 through the connection 132. The performance data monitoring software 134 gathers and stores performance data and forwards this to the optimizer 138 which further stores the data in the performance data file 136. This performance data 136 also may serve as an input to the optimizer 138 which attempts to enhance the performance of I/O operations, such as those I/O operations associated with PSDs 16 a-16 n of the system 12. The optimizer 138 may take into consideration various types of parameters and performance data 136 in an attempt to optimize particular metrics associated with performance of the data storage system 12. The performance data 136 may be used by the optimizer to determine metrics described and used in connection with techniques herein. The optimizer may access the performance data, for example, collected for a plurality of LVs when performing a data storage optimization. The performance data 136 may be used in determining a workload for one or more PSDs and/or VSUs, including logical devices or volumes (LVs) serving as data devices, thin devices) or other virtually provisioned devices, portions of thin devices, and the like. The workload also may be a measurement or level of “how busy” a PSD or VSU is, for example, in terms of I/O operations (e.g., I/O throughput such as number of IOs/second, response time (RT), and the like).

The response time for a PSD or VSU may be based on a response time associated with the PSD or VSU for a period of time. The response time may be based on read and write operations directed to the PSD or VSU. Response time represents the amount of time it takes the data storage system to complete an I/O request (e.g., a read or write request). Response time may be characterized as including two components: service time and wait time. Service time is the actual amount of time spent servicing or completing an I/O request after receiving the request from a host via an HA 21, or after the data storage system 12 generates the I/O request internally. The wait time is the amount of time the I/O request spends waiting in line or queue waiting for service (e.g., prior to executing the I/O operation).

It should be noted that the operations of read and write with respect to a VSU may be viewed as read and write requests or commands from the DA 23, controller or other backend PSD interface. Thus, these operations also may be characterized as a number of operations with respect to the PSD (e.g., number of PSD reads, writes, and the like, based on PSD accesses). This is in contrast to observing or counting a number of particular types of I/O requests (e.g., reads or writes) as issued from the host and received by a front-end component such as an HA 21. To illustrate, a host read request may not result in a read request or command issued to the DA if there is a cache hit and the requested data is in cache. The host read request results in a read request or command issued to the DA 23 to retrieve data from the disk drive only if there is a read miss. Furthermore, when writing data of a received host I/O request to the PSD, the host write request may result in multiple reads and/or writes by the DA 23 in addition to writing out the host or user data of the request. For example, if the data storage system implements a RAID data protection technique, such as RAID-5, additional reads and writes may be performed such as in connection with writing out additional parity information for the user data. Thus, observed data gathered to determine workload, such as observed numbers of reads and writes, may refer to the read and write requests or commands performed by the DA. Such read and write commands may correspond, respectively, to PSD accesses such as disk reads and writes that may result from a host I/O request received by an HA 21.

The optimizer 138 may perform processing of the techniques herein set forth in following paragraphs to determine how to allocate or partition physical storage in a multi-tiered environment for use by multiple applications. The optimizer 138 also may perform other processing such as, for example, to determine what particular portions of thin devices to store on PSDs of a particular tier, evaluate when to migrate or move data between PSDs of different tiers, and the like. It should be noted that the optimizer 138 may generally represent one or more components that perform processing as described herein as well as one or more other optimizations and other processing that may be performed in an embodiment.

Described in the following paragraphs are techniques that may be performed to determine promotion and demotion thresholds (described below in more detail) used in determining what data portions of thin devices to store on PSDs of a particular tier in a multi-tiered storage environment. Such data portions of a thin device may be automatically placed in a storage tier where the techniques herein have determined the storage tier is best to service that data in order to improve data storage system performance. The data portions also may be automatically relocated or migrated to a different storage tier as the workload and observed performance characteristics for the data portions change over time. In accordance with techniques herein, analysis of performance data for data portions of thin devices may be performed in order to determine whether particular data portions should have their data contents stored on PSDs located in a particular storage tier. The techniques herein may take into account how “busy” the data portions are in combination with defined capacity limits and defined performance limits (e.g., such as I/O throughput or I/Os per unit of time, response time, utilization, and the like) associated with a storage tier in order to evaluate which data to store on PSDs of the storage tier. The foregoing defined capacity limits and performance limits may be used as criteria to determine promotion and demotion thresholds based on projected or modeled I/O workload of a storage tier. Different sets of performance limits, also referred to as comfort performance zones or performance zones, may be evaluated in combination with capacity limits based on one or more overall performance metrics (e.g., average response time across all storage tiers for one or more storage groups) in order to select the promotion and demotion thresholds for the storage tiers.

Promotion may refer to movement of data from a first storage tier to a second storage tier where the second storage tier is characterized as having PSDs of higher performance than PSDs of the first storage tier. Demotion may refer generally to movement of data from a first storage tier to a second storage tier where the first storage tier is characterized as having PSDs of higher performance than PSDs of the second storage tier. As such, movement of data from a first tier of flash devices to a second tier of high-speed disk devices and/or low-speed disk devices may be characterized as a demotion and movement of data from the foregoing second tier to the first tier a promotion. The promotion and demotion thresholds refer to thresholds used in connection with data movement.

As described in following paragraphs, one embodiment may use an allocation policy specifying an upper limit or maximum threshold of storage capacity for each of one or more tiers for use with an application. The partitioning of physical storage of the different storage tiers among the applications may be initially performed using techniques herein in accordance with the foregoing thresholds of the application's allocation policy and other criteria. In accordance with techniques herein, an embodiment may determine amounts of the different storage tiers used to store an application's data, and thus the application's storage group, subject to the allocation policy and other criteria. Such criteria also may include one or more performance metrics indicating a workload of the application. For example, an embodiment may determine one or more performance metrics using collected or observed performance data for a plurality of different VSUs, and/or portions thereof, used by the application. Thus, the partitioning of the different storage tiers among multiple applications also may take into account the workload or how “busy” an application is. Such criteria also may include capacity limits specifying how much of each particular storage tier may be used to store data for the application's VSUs. As described in various embodiments herein, the criteria may include one or more performance metrics in combination with capacity limits, performance metrics alone without capacity limits, or capacity limits alone without performance metrics. Of course, as will be appreciated by those of ordinary skill in the art, such criteria may include any of the foregoing in combination with other suitable criteria.

As an example, the techniques herein may be described with reference to a storage environment having three storage tiers—a first tier of only SSDs in the data storage system, a second tier of only high-speed disk drives, and a third tier of only low-speed disk drives. In terms of performance, the foregoing three tiers may be ranked from highest to lowest as follows: first, second, and then third. The lower the tier ranking, the lower the tier's performance characteristics (e.g., longer latency times, capable of less I/O throughput/second/GB (or other storage unit), and the like). Generally, different types of PSDs have different types of characteristics. There are different reasons why one may want to use one storage tier and type of PSD over another depending on criteria, goals and the current performance characteristics exhibited in connection with performing I/O operations. For example, flash drives of the first tier may be a best choice or candidate for storing data which may be characterized as I/O intensive, “hot” or “busy” thereby experiencing a high rate of I/Os to frequently access the PSD containing the LV's data. However, flash drives tend to be expensive in terms of storage capacity. Low-speed disk drives may be a best choice or candidate for storing data of applications requiring a large storage capacity and which are not I/O intensive with respect to access and retrieval from the PSD (i.e., are “cold”). The second tier of high-speed disk drives may be characterized as “in between” flash drives and low-speed disk drives in terms of cost/GB and I/O performance. Thus, in terms of relative performance characteristics, flash drives may be characterized as having higher performance than both high-speed and low-speed disks, and high-speed disks may be characterized as having a higher performance than low-speed disks.

Since flash drives of the first tier are the best suited for high throughput/sec/GB, processing may be performed to determine which of the applications, and portions thereof, are characterized as most I/O intensive and therefore may be good candidates to have their data stored on flash drives. Similarly, the second most I/O intensive applications, and portions thereof, may be good candidates to store on high-speed disk drives of the second tier and the least I/O intensive applications may be good candidates to store on low-speed disk drives of the third tier. As such, workload for an application may be determined using some measure of I/O intensity, performance or activity (e.g., I/O throughput/second, percentage of read operation, percentage of write operations, response time, etc.) of each VSU or PSD used for the application's data. Some measure of workload may be used as a factor or criterion in combination with others described herein for determining what data portions are located on the PSDs of each of the different storage tiers.

FIG. 4 is a schematic illustration showing a data storage system 150 that may be used in connection with an embodiment of the system described herein. The data storage system 150 may include a storage array 124 having multiple directors 130-132 and multiple storage volumes (LVs, logical devices or VOLUMES 0-3) 110-113. Host applications 140-144 and/or other entities (e.g., other storage devices, SAN switches, etc.) request data writes and data reads to and from the storage array 124 that are facilitated using one or more of the directors 130-132. The storage array 124 may include similar features as that discussed above.

The volumes 110-113 may be provided in multiple storage tiers (TIERS 0-3) that may have different storage characteristics, such as speed, cost, reliability, availability, security and/or other characteristics. As described above, a tier may represent a set of storage resources, such as PSUs, residing in a storage platform. Examples of storage disks that may be used as storage resources within a storage array of a tier may include sets of low-speed disks, high-speed disks and/or EFDs, among other known types of storage devices.

According to various embodiments, each of the volumes 110-113 may be located in different storage tiers. Tiered storage provides that data may be initially allocated to a particular fast volume/tier, but a portion of the data that has not been used over a period of time (for example, three weeks) may be automatically moved to a slower (and perhaps less expensive) tier. For example, data that is expected to be used frequently, for example database indices, may be initially written directly to fast storage whereas data that is not expected to be accessed frequently, for example backup or archived data, may be initially written to slower storage. In an embodiment, the system described herein may be used in connection with a Fully Automated Storage Tiering (FAST) product produced by EMC Corporation of Hopkinton, Mass., that The techniques herein may be used to determine amounts or allocations of each storage tier used by each application based on capacity limits in combination with performance limits.

Referring to FIG. 5A, shown is a schematic diagram of the storage array 124 as including a plurality of data devices 61-67 communicating with directors 131-133. The data devices 61-67 may be implemented as logical devices like standard logical devices (also referred to as thick devices) provided in a Symmetrix® storage system produced by EMC Corporation of Hopkinton, Mass., for example. In some embodiments, the data devices 61-67 may not be directly useable (visible) to hosts coupled to the storage array 124. Each of the data devices 61-67 may correspond to a portion (including a whole portion) of one or more of the disk drives 42-44 (or more generally PSUs). Thus, for example, the data device section 61 may correspond to the disk drive 42, may correspond to a portion of the disk drive 42, or may correspond to a portion of the disk drive 42 and a portion of the disk drive 43. The data devices 61-67 may be designated as corresponding to different classes, so that different ones of the data devices 61-67 correspond to different physical storage having different relative access speeds or RAID protection type (or some other relevant distinguishing characteristic or combination of characteristics), as further discussed elsewhere herein. Alternatively, in other embodiments that may be used in connection with the system described herein, instead of being separate devices, the data devices 61-67 may be sections of one data device.

As shown in FIG. 5B, the storage array 124 may also include a plurality of thin devices 71-74 that may be adapted for use in connection with the system described herein when using thin provisioning. In a system using thin provisioning, the thin devices 71-74 may appear to a host coupled to the storage array 124 as one or more logical volumes (logical devices) containing contiguous blocks of data storage. Each of the thin devices 71-74 may contain pointers to some or all of the data devices 61-67 (or portions thereof). As described in more detail elsewhere herein, a thin device may be virtually provisioned in terms of its allocated physical storage in physical storage. That is, a thin device presented to a host as having a particular capacity may be allocated physical storage as needed, rather than allocated physical storage according to the entire thin device capacity defined upon creation of the thin device. As such, a thin device presented to the host as having a capacity with a corresponding LBA (logical block address) range may have portions of the LBA range for which storage is not allocated.

Referring to FIG. 5C, shown is a diagram 150 illustrating tables that are used to keep track of device information. A first table 152 corresponds to all of the devices used by a data storage system or by an element of a data storage system, such as an HA 21 and/or a DA 23. The table 152 includes a plurality of logical device (logical volume) entries 156-158 that correspond to all the logical devices used by the data storage system (or portion of the data storage system). The entries in the table 152 may include information for thin devices, for data devices (such as logical devices or volumes), for standard logical devices, for virtual devices, for BCV devices, and/or any or all other types of logical devices used in connection with the system described herein.

Each of the entries 156-158 of the table 152 correspond to another table that may contain information for one or more logical volumes, such as thin device logical volumes. For example, the entry 157 may correspond to a thin device table 162. The thin device table 162 may include a header 164 that contains overhead information, such as information identifying the corresponding thin device, information concerning the last used data device and/or other information including counter information, such as a counter that keeps track of used group entries (described below). The header information, or portions thereof, may be available globally to the data storage system.

The thin device table 162 may include one or more group elements 166-168, that contain information corresponding to a group of tracks on the data device. A group of tracks may include one or more tracks, the number of which may be configured as appropriate. In an embodiment herein, each group has sixteen tracks, although this number may be configurable.

One of the group elements 166-168 (for example, the group element 166) of the thin device table 162 may identify a particular one of the data devices 61-67 having a track table 172 that contains further information, such as a header 174 having overhead information and a plurality of entries 176-178 corresponding to each of the tracks of the particular one of the data devices 61-67. The information in each of the entries 176-178 may include a pointer (either direct or indirect) to the physical address on one of the physical disk drives of the data storage system that maps to the logical address(es) of the particular one of the data devices 61-67. Thus, the track table 162 may be used in connection with mapping logical addresses of the logical devices corresponding to the tables 152, 162, 172 to physical addresses on the disk drives or other PSUs of the data storage system.

The tables 152, 162, 172 may be stored in the global memory 25 b of the data storage system. In addition, the tables corresponding to particular logical devices accessed by a particular host may be stored (cached) in local memory of the corresponding one of the HA's. In addition, an RA and/or the DA's may also use and locally store (cache) portions of the tables 152, 162, 172.

Referring to FIG. 5D, shown is a schematic diagram illustrating a group element 166 of the thin device table 162 in connection with an embodiment of the system described herein. The group element 166 may include a plurality of entries 166 a-166 f. The entry 166 a may provide group information, such as a group type that indicates whether there has been physical address space allocated for the group. The entry 166 b may include information identifying one (or more) of the data devices 61-67 that correspond to the group (i.e., the one of the data devices 61-67 that contains pointers for physical data for the group). The entry 166 c may include other identifying information for the one of the data devices 61-67, including a speed indicator that identifies, for example, if the data device is associated with a relatively fast access physical storage (e.g., SSD) or a relatively slow access physical storage (e.g., 7.2K RPM drive). Other types of designations of data devices are possible (e.g., relatively expensive or inexpensive). The entry 166 d may be a pointer to a head of the first allocated track for the one of the data devices 61-67 indicated by the data device ID entry 166 b. Alternatively, the entry 166 d may point to header information of the data device track table 172 immediately prior to the first allocated track. The entry 166 e may identify a cylinder of a first allocated track for the one the data devices 61-67 indicated by the data device ID entry 166 b. The entry 166 f may contain other information corresponding to the group element 166 and/or the corresponding thin device. In other embodiments, entries of the group table 166 may identify a range of cylinders of the thin device and a corresponding mapping to map cylinder/track identifiers for the thin device to tracks/cylinders of a corresponding data device. In an embodiment, the size of table element 166 may be eight bytes.

Accordingly, a thin device presents a logical storage space to one or more applications running on a host where different portions of the logical storage space may or may not have corresponding physical storage space associated therewith. However, the thin device is not mapped directly to physical storage space. Instead, portions of the thin storage device for which physical storage space exists are mapped to data devices, which are logical devices that map logical storage space of the data device to physical storage space on the disk drives or other PSUs. Thus, an access of the logical storage space of the thin device results in either a null pointer (or equivalent) indicating that no corresponding physical storage space has yet been allocated, or results in a reference to a data device which in turn references the underlying physical storage space.

Thin devices and thin provisioning are described in more detail in U.S. Pat. No. 9,152,349, issued Oct. 6, 2015, “Automated Information Life-Cycle Management With Thin Provisioning,” Yochai, and U.S. Pat. No. 7,949,637, issued May 24, 2011, “Storage Management for Fine Grained Tiered Storage with Thin Provisioning”, to Burke, both of which are incorporated by reference herein.

As discussed elsewhere herein, the data devices 61-67 (and other logical devices) may be associated with physical storage areas (e.g., disk drives, tapes, solid state storage, etc.) having different characteristics. In various embodiments, the physical storage areas may include multiple tiers of storage in which each sub-tier of physical storage areas and/or disk drives may be ordered according to different characteristics and/or classes, such as speed, technology and/or cost. The devices 61-67 may appear to a host coupled to the storage array 124 as a logical volume (logical device) containing a contiguous block of data storage, as discussed herein. Accordingly, each of the devices 61-67 may map to storage areas across multiple PSUs. The granularity at which a data storage system described herein operates may be smaller than at the file level, for example potentially as small as a single byte, but more practically at the granularity of a single logical block or collection of sequential data blocks. A data block may be of any size including file system or database logical block size, physical block, track or cylinder and/or other size. Multiple data blocks may be substantially the same size or different sizes, such as different size data blocks for different storage volumes or different sized data blocks within a single storage volume.

In accordance with techniques herein, an embodiment may allow for locating all of the data of a single logical portion or entity in a same tier or in multiple different tiers depending on the logical data portion or entity. In an embodiment including thin devices, the techniques herein may be used where different portions of data of a single thin device may be located in different storage tiers. For example, a thin device may include two data portions and a first of these two data portions may be identified as a “hot spot” of high I/O activity (e.g., having a large number of I/O accesses such as reads and/or writes per unit of time) relative to the second of these two portions. As such, an embodiment in accordance with techniques herein may have added flexibility in that the first portion of data of the thin device may be located in a different higher performance storage tier than the second portion. For example, the first portion may be located in a tier comprising flash devices and the second portion may be located in a different tier of high-speed or low-speed drives.

Referring to FIG. 6, shown is an example illustrating information that may be defined and used in connection with techniques herein. The example 200 includes multiple storage tiers 206, 208, and 210, an allocation policy (AP) 204, and storage group (SG) 202. The SG 202 may include one or more thin devices (TDs), such as TD A 220 and TD B 222, used by an application 230. The application 230 may execute, for example, on one of the hosts of FIG. 1. The techniques herein may be used to determine how to partition physical storage of the multiple storage tiers 206, 208 and 210 for use in storing or locating the application's data, such as data of the TDs 220 and 222. It should be noted that the particular number of tiers, TDs, and the like, should not be construed as a limitation. An SG may represent a logical grouping of TDs used by a single application although an SG may correspond to other logical groupings for different purposes. An SG may, for example, correspond to TDs used by multiple applications.

Each of 206, 208 and 210 may correspond to a tier definition as described elsewhere herein. Element 206 represents a first storage tier of flash drives having a tier capacity limit C1. Element 208 represents a first storage tier of high-speed disk drives having a tier capacity limit C2. Element 210 represents a first storage tier of low-speed disk drives having a tier capacity limit C3. Each of C1, C2 and C3 may represent an available or maximum amount of storage capacity in the storage tier that may be physical available in the system. The AP 204 may be associated with one of more SGs such as SG 202. The AP 204 specifies, for an associated SG 202, a capacity upper limit or maximum threshold for one or more storage tiers. Each such limit may identify an upper bound regarding an amount of storage that may be allocated for use by the associated SG. The AP 204 may be associated with one or more of the storage tiers 206, 208 and 210 that may be defined in a multi-tier storage environment. The AP 204 in this example 200 includes limit 204 a identifying a maximum or upper limit of storage for tier1, limit 204 b identifying a maximum or upper limit of storage for tier2, and limit 204 c identifying a maximum or upper limit of storage for tier3. The SG 202 may be based on an SG definition identifying 202 a the logical devices, such as TDs included in the SG.

In connection with techniques herein, the maximum limits 204 a, 204 b and 204 c each represent an upper bound of a storage capacity to which an associated SG is subjected to. The techniques herein may be used to partition less than the amount or capacity represented by such limits. An amount of physical storage of a tier allocated for use by an application is allowed to vary up to the tier limit as defined in the AP 204 in accordance with other criteria associated with the application such as, for example, varying application workload. The optimizer may vary the amount of storage in each tier used by an SG202, and thus an application, based on workload and possibly other criteria when performing a cost benefit analysis, where such amounts are subject to the limits of the SG's AP and also performance limits described in more detail elsewhere herein. At a second point in time, the workloads and possibly other criteria for the applications may change and the optimizer may repartition the storage capacity used by each application subject to the capacity limits of APs and performance limits.

Referring to FIG. 7, shown is an example which more generally illustrates different associations between SGs, APs and tiers in an embodiment in accordance with techniques herein. The example 350 illustrates that an embodiment may have multiple storage tiers (e.g., tiers 1-N), multiple APs (e.g., AP1-N), and multiple SGs (e.g., SG 1-M). Each AP may be associated with one or more of the storage tiers. Each AP may also be associated with different tiers than other APs. For example, APn is associated with Tier N but AP1 is not. For each tier associated with an AP, the AP may define a maximum capacity limit as described in connection with FIG. 6. Each AP may be associated with one or more SGs. For example SGs1-N may be associated with a same AP1, and SGs N+1 through M may be associated with a same APn.

With reference back to FIG. 6, each of the maximum capacity limits may have any one of a variety of different forms. For example, such limits may be expressed as a percentage or portion of tier total storage capacity (e.g., such as a percentage of C1, C2, or C3), as an integer indicating an amount or quantity of storage 410 c (e.g., indicating a number of bytes or other number of storage units), and the like.

Data used in connection with techniques herein, such as the performance data of FIG. 3 used in determining device and SG workloads, may be obtained through observation and monitoring actual performance. Data may also be determined in other suitable ways such as, for example, through simulation, estimation, and the like. Observed or collected data may be obtained as described in connection with FIG. 3 by monitoring and recording one or more aspects of I/O activity for each TD, and portions thereof. For example, for each TD, and/or portions thereof, an average number of reads occurring within a given time period may be determined, an average number of writes occurring within a given time period may be determined, an average number of read misses occurring within a given time period may be determined, and the like. It should be noted that the operations of read and write with respect to a TD may be viewed as read and write requests or commands from the DA, controller or other backend physical device interface. Thus, these operations may also be characterized as an average number of operations with respect to the PSU (e.g., average number of physical device reads, writes, and the like, based on physical device accesses). This is in contrast to observing or counting a number of particular types of I/O requests (e.g., reads or writes) as issued from the host and received by a front-end component. To illustrate, a host read request may not result in a read request or command issued to the DA if there is a cache hit and the requested data is in cache. The host read request results in a read request or command issued to the DA to retrieve data from the physical drive only if there is a read miss. Furthermore, when writing data of a received host I/O request to the physical device, the host write request may result in multiple reads and/or writes by the DA in addition to writing out the host or user data of the request. For example, if the data storage system implements a RAID data protection technique, such as RAID-5, additional reads and writes may be performed such as in connection with writing out additional parity information for the user data. Thus, observed data gathered to determine workload, such as observed numbers of reads and writes, may refer to the read and write requests or commands performed by the DA. Such read and write commands may correspond, respectively, to physical device accesses such as disk reads and writes that may result from a host I/O request received by an FA.

It should be noted that movement of data between tiers from a source tier to a target tier may include determining free or unused storage device locations within the target tier. In the event there is an insufficient amount of free of unused storage in the target tier, processing may also include displacing or relocating other data currently stored on a physical device of the target tier. An embodiment may perform movement of data to and/or from PSUs using any suitable technique. Also, any suitable technique may be used to determine a target storage device in the target tier where the data currently stored on the target is relocated or migrated to another physical device in the same or a different tier.

One embodiment in accordance with techniques herein may include multiple storage tiers including a first tier of flash devices and one or more other tiers of non-flash devices having lower performance characteristics than flash devices. The one or more other tiers may include, for example, one or more types of disk devices. The tiers may also include other types of SSDs besides flash devices.

As described above, a thin device (also referred to as a virtual provision device) is a device that represents a certain capacity having an associated address range. Storage may be allocated for thin devices in chunks or data portions of a particular size as needed rather than allocate all storage necessary for the thin device's entire capacity. Therefore, it may be the case that at any point in time, only a small number of portions or chunks of the thin device actually are allocated and consume physical storage on the back-end (on physical disks, flash or other PSUs). A thin device may be constructed of chunks having a size that may vary with embodiment. For example, in one embodiment, a chunk may correspond to a group of 12 tracks (e.g., 12 tracks*64 Kbytes/track=768 Kbytes/chunk). As also noted with a thin device, the different chunks may reside on different data devices in one or more storage tiers. In one embodiment, as will be described below, a storage tier may consist of one or more storage pools. Each storage pool may include multiple LVs and their associated PSUs. With thin devices, a system in accordance with techniques herein has flexibility to relocate individual chunks as desired to different devices in the same as well as different pools or storage tiers. For example, a system may relocate a chunk from a flash storage pool to a low-speed storage pool. In one embodiment using techniques herein, a thin device can be bound to a particular storage pool of a storage tier at a point in time so that any chunks requiring allocation of additional storage, such as may occur when writing data to the thin device, result in allocating storage from this storage pool. Such binding may change over time for a thin device.

A thin device may contain thousands and even hundreds of thousands of such chunks. As such, tracking and managing performance data such as one or more performance statistics for each chunk, across all such chunks, for a storage group of thin devices can be cumbersome and consume an excessive amount of resources. Described in following paragraphs are techniques that may be used in connection with collecting performance data about thin devices where such information may be used to determine which chunks of thin devices are most active relative to others. Such evaluation may be performed in connection with determining promotion/demotion thresholds use in evaluating where to locate and/or move data of the different chunks with respect to the different storage tiers in a multi-storage tier environment. In connection with examples in following paragraphs, details such as having a single storage pool in each storage tier, a single storage group, and the like, are provided for purposes of illustration. Those of ordinary skill in the art will readily appreciate the more general applicability of techniques herein in other embodiments such as, for example, having a storage group including a plurality of storage pools, and the like.

Referring to FIG. 8A, shown is an example 700 illustrating use of a thin device in an embodiment in accordance with techniques herein. The example 700 includes three storage pools 712, 714 and 716 with each such pool representing a storage pool of a different storage tier. For example, pool 712 may represent a storage pool of tier A of flash storage devices, pool 714 may represent a storage pool of tier B of high-speed storage devices, and pool 716 may represent a storage pool of tier C of low-speed storage devices. Each storage pool may include a plurality of logical devices and associated PSUs (or portions thereof) to which the logical devices are mapped. Element 702 represents the thin device address space or range including chunks which are mapped to different storage pools. For example, element 702 a denotes a chunk C1 which is mapped to storage pool 712 and element 702 b denotes a chunk C2 which is mapped to storage pool 714. Element 702 may be a representation for a first thin device which is included in a storage group of one or more thin devices.

It should be noted that although the example 700 illustrates only a single storage pool per storage tier, an embodiment may also have multiple storage pools per tier.

Referring to FIG. 8B, shown is an example representation of information that may be included in an allocation map in an embodiment in accordance with techniques herein. An allocation map may be used to identify the mapping for each thin device (TD) chunk (e.g. where each chunk is physically located). Element 760 represents an allocation map that may be maintained for each TD. In this example, element 760 represents information as may be maintained for a single TD although another allocation map may be similarly used and maintained for each other TD in a storage group. Element 760 may represent mapping information as illustrated in FIG. 8A such as in connection the mapping of 702 to different storage pool devices. The allocation map 760 may contain an entry for each chunk and identify which LV and associated physical storage is mapped to the chunk. For each entry or row of the map 760 corresponding to a chunk, a first column 760 a, Chunk ID, denotes an identifier to uniquely identify the chunk of the TD, a second column 760 b, indicates information about the LV and offset to which the chunk is mapped, and a third column storage pool 760 c denotes the storage pool and tier including the LV of 760 b. For example, entry 762 represents chunk C1 illustrated in FIG. 8A as 702 a and entry 764 represents chunk C2 illustrated in FIG. 8A as 702 b. It should be noted that although not illustrated, the allocation map may include or otherwise use other tables and structures which identify a further mapping for each LV such as which physical device locations map to which LVs. This further mapping for each LV is described and illustrated elsewhere herein such as, for example, with reference back to FIG. 5B. Such information as illustrated and described in connection with FIG. 8B may be maintained for each thin device in an embodiment in accordance with techniques herein.

In connection with collecting statistics characterizing performance, workload and/or activity for a thin device, one approach may be to collect the information per chunk or, more generally, for the smallest level of granularity associated with allocation and de-allocation of storage for a thin device. Such statistics may include, for example, a number of reads/unit of time, #writes/unit of time, a number of pre-fetches/unit of time, and the like. However, collecting such information at the smallest granularity level does not scale upward as number of chunks grows large such as for a single thin device which can have up to, for example 300,000 chunks.

Therefore, an embodiment in accordance with techniques herein may collect statistics on a grouping of “N” chunks also referred to as an extent, where N represents an integer number of chunks, N>0. N may be, for example, 480 in one embodiment. Each extent may represent a consecutive range or portion of the thin device in terms of thin device locations (e.g., portion of the address space or range of the thin device). Note that the foregoing use of consecutive does not refer to physical storage locations on PSUs but rather refers to consecutive addresses with respect to a range of addresses of the thin device which are then mapped to physical device locations which may or may not be consecutive, may be on the same or different PSUs, and the like. For example, in one embodiment, an extent may be 480 chunks (N=480) having a size of 360 MBs (megabytes).

An extent may be further divided into sub extents, where each sub extent is a collection of M chunks. M may be, for example 10 in one embodiment. In one embodiment, the sub-extent size may correspond to the smallest granularity of data movement. In other words, the sub extent size represents the atomic unit or minimum amount of data that can be operated upon when performing a data movement such as between storage tiers.

Referring to FIG. 9, shown is an example illustrating partitioning of a thin device's address space or range in an embodiment in accordance with techniques herein. The example 250 includes a thin device address space or range 252 which, as described elsewhere herein, includes chunks mapped to physical storage locations. The thin device address space or range 252 may be partitioned into one or more extents 254 a-254 n. Each of the extents 254 a-254 n may be further partitioned into sub-extents. Element 260 illustrates that extent X 254 n may include sub extents 256 a-256 n. Although only detail is illustrated for extent 254 n, each of the other extents of the thin device also includes a same number of sub extents as illustrated for 254 n. Each of the sub extents 256 a-256 n may represent a grouping of “M” chunks. Element 262 illustrates that sub extent 1 256 a may include chunks 258 a-258 n. Although only detail is illustrated for sub extent 256 a, each of the other sub extents 256 b-256 n also includes a same number of “M” chunks as illustrated for 256 a. Thus, each of the extents 254 a-254 n may represent an grouping of “N” chunks, where N=#sub extents/extent*M chunks/sub extent  EQUATION 1

An embodiment in accordance with techniques herein may collect statistics for each extent and also other information characterizing activity of each sub extent of a thin device. Statistics for each extent may be characterized as either long term or short term. Short term refers to statistics which may reflect performance, workload, and/or I/O activity of an extent with respect to a relatively short window of time. Thus, short term statistics may reflect recent extent activity for such a short time period. In contrast and relative to short term, long term refers to statistics reflecting performance, workload and/or I/O activity of an extent with respect to a longer period of time. Depending on the evaluation being performed, such as by the optimizer, it may be desirable to place greater weight on short term information than long term, or vice versa. Furthermore, the information maintained per sub extent may be used as needed once particular extents of interest have been identified.

Referring to FIG. 10, shown is an example of information that may be collected and used in connection each extent in an embodiment in accordance with techniques herein. The example 300 illustrates that short term information 302, long term information 304 and a sub extent activity bitmap 306 may be collected for each extent. The short term information 302 and long term information 304 may be used in connection with determining short term rates 320 and long term rates 330 for each extent. The statistics included in 302, 304, 320 and 330 may reflect activity with respect to the entire extent. The activity bitmap 306 is illustrated in further detail by element 307 as including an entry for each sub extent in the associated extent. Entries of 307 are denoted by A, B, C, and the like. Each of the entries of 307 represents aggregated or collective activity information for a corresponding sub extent denoted by the numeric identifiers 307 a of 1, 2, 3, etc. Each entry of 307 may include one or more bits used to encode an activity level with respect to all chunks of a corresponding sub-extent. For example, the entry of 307 denoted as A represents an activity level for all chunks in sub extent 1. An embodiment may use any number of bits for each entry of the activity bitmap 306, 307. For example, in one embodiment, each entry of the activity bitmap may be 2 bits capable of representing any of 4 integer values—0, 1, 2, and 3.

As will be described in following paragraphs, the short term rates 320, long term rates 330 and sub extent activity bitmap 306 may be used in connection with a variety of different evaluations such as by the optimizer 138. Generally, the activity level information or data for an extent such as illustrated in FIG. 10 may be referred to as extent activity level information including one or more metrics indicating an activity level for the extent. The extent activity level information may comprise short term activity information (e.g., such as 302 and/or 320) and long term activity information (e.g., such as 304 and 330).

In one embodiment, the short term rates 320 for an extent may include a read miss rate (e.g., random read miss (RRM) rate) 322, a write I/O rate 324 and a pre-fetch rate 326 for the extent. The long term rates 330 for an extent may include a read miss rate 332 (e.g., number of read misses/unit of time, where a read miss refers to a cache miss for a read), a write I/O rate 334 (e.g., number of writes/unit of time) and a pre-fetch rate 336 (e.g., number of pre-fetches/unit of time) for the extent. As known in the art, data may be pre-fetched from a physical device and placed in cache prior to reference or use with an I/O operation. For example, an embodiment may perform sequential stream I/O recognition processing to determine when consecutive portions of a thin device are being referenced. In this case, data of the sequential stream may be pre-fetched from the physical device and placed in cache prior to usage in connection with a subsequent I/O operation. In connection with a portion of data at a first point in a sequential stream associated with a current I/O operation, data subsequent to the first point may be pre-fetched such as when obtaining the portion from a physical device in anticipation of future usage with subsequent I/Os. The short term pre-fetch rate 326, as well as the long term pre-fetch rate 336, may also be referred to as denoting a number of sequential reads or sequential read miss operations performed since such pre-fetching may occur in response to determination that a read operation is performed for data which is not in cache (read miss) and the read operation is for data included in a series of sequentially read data portions as described above. The read miss rates 322 and 332 may represent random read miss (RRM) rates where such read misses (e.g., data requested not currently in cache) are associate with read operations not included in connection with reading data of a sequential stream (e.g., all read misses not used in connection with computing 326 and 336).

Each of the foregoing rates of 320 and 330 may be with respect to any unit of time, such as per second, per hour, and the like. In connection with describing elements 302 and 304 in more detail, what will be described is how an embodiment in accordance with techniques herein may determine the short term rates 320 and long term rates 330 using a decay function and decay coefficients.

In an embodiment in accordance with techniques herein, a decay coefficient may be characterized as a weighting factor given to previous activity information. The higher the coefficient, the greater the weight given to previous activity information for the extent. Thus, the adjusted activity level of an extent at a current time, “An”, may be generally represented as a function of a current observed or actual activity level for the current time, “a_(n)”, a decay coefficient, “r”, and previous adjusted activity level for the previous time period or sampling period, “A_(n-1)”. In connection with the foregoing, “A” may represent an adjusted activity level, “n” may denote the current time period or sampling period and “n−1” may denote the immediately prior or previous time period or sampling period at which the activity for the extent was determined. In other words, “a_(n)” is adjusted to take into account previous activity as represented by “A_(n-1)” and “An” represents the resulting adjusted value of “a_(n)”. With respect to a statistic or metric such as a number or read misses, “a_(n)” and “An” may each represent an integer quantity or number of read misses within a current sampling period, “n”. The foregoing may generally be represented as: An=a _(n)+(r*A _(n-1))  EQUATION 2 wherein

a_(n) is the actual observed activity metric for the current or “nth” sampling period,

“r” is a decay coefficient,

“A_(n)” is the adjusted activity metric for the current or “nth” sampling period, and

“A_(n-1)” is the adjusted activity metric from the previous or “n−1” sampling period.

Beginning with an initial time period or sampling period, denoted by i=“0” (zero), the adjusted activity A0 may be initially that which is observed, a0. Subsequent observed or actual activity levels may be adjusted as described above. Generally, “a_(i)” may denote an actual or observed value obtained for an activity metric for a sampling period “i”, where “i” is an integer greater than or equal to 0. “Ai” may similarly denote an adjusted activity metric (or adjusted value for “a_(i)”) for a sampling period “i”, where “i” is an integer greater than or equal to 0. Thus, for consecutive sample periods at which actual or observed activity metrics are obtained (as denoted by lower case “a_(i)”s), corresponding adjusted activity levels (e.g., “A” values) may be determined as follows:

A0=a0 /* Adjusted activity level A0, at time=0 or initially */

A1=a1+(r*A0) /* Adjusted activity level A1, at first sampling period, i=1 */

A2=a2+(r*A1) /* Adjusted activity level A2, at second sampling period, i=2 */

and so on for subsequent sampling periods 3, 4, and the like, based on EQUATION 2.

In connection with EQUATION 2, 0<=r<1, where “r” is a decay coefficient or weight given to previous activity. Varying “r” in EQUATION 2 results in accordingly varying the weight given to past or previous activity. If r=0, then no weight is given to previous or historic values. Thus, the closer “r” is to 0, the lesser weight given to previous activity. Similarly, the closer “r” is to 1, the greater the weight given to previous activity. In connection with determining an adjusted activity level, An, using EQUATION 2 for short term and long term, different decay coefficients may be selected. Generally “r” for short term is less than “r” used in connection with long term activity. For example, in one embodiment, “r” used in connection short term activity levels may be 50% or 0.50 or smaller. “r” used in connection with long term activity levels may be 80% or 0.80 or larger. The foregoing are exemplary values that may be selected for “r” in connection with short term and long term activity levels depending on the weight to be given to previous activity. In connection with short term activity, a decay coefficient may be selected in accordance with providing a relatively short term rate of decay for an activity level metric determined at a point in time. For example, a short term rate of decay may provide for a rate of decay for an activity level metric on the order of one or more hours (e.g., less than a day). In connection with long term activity, a decay coefficient may be selected in accordance with providing a relatively long term rate of decay for an activity level metric determined at a point in time. For example, a long term rate of decay may provide for a rate of decay for an activity level metric on the order of one or more days, a week, and the like. Thus, an activity metric at a first point in time may have a weighted or residual effect on an adjusted activity level determined at a later point in time in accordance with the selected decay coefficient indicating the rate of decay of the activity metric.

As mentioned above, EQUATION 2 results in a metric or count, such as a number of read misses, number of writes, or number or pre-fetches during a sample period. It may be desirable to also determine a rate with respect to a unit of time, such as per second, per hour, and the like, for each of the foregoing adjusted activity metrics An. A rate with respect to a unit of time for the adjusted activity level An may be represented as: Ar=An*(1−r)/(1−r ^(n-1))  EQUATION 3 where Ar=the adjusted activity rate per unit of time,

r=decay coefficient or weight as described above,

n=denotes an “nth” sampling period as described above,

An=adjusted activity level determined for a given sampling period “n” (e.g. using EQUATION 2 as described above).

Generally, the higher the decay coefficient, r, the slower the change in Ar as may be the desired case with long term Ar values. Thus an embodiment may select decay coefficients for use with long term and short term Ar values so that, when plotted with respect to time, long term Ar values generally have a smaller slope than that associated with short term Ar values.

Referring to FIG. 11, shown is an example graphically illustrating the general shape of curves for long term (LT) and short term (ST) values in an embodiment in accordance with techniques herein. The activity level values (Y-axis values) are plotted with respect to time (X-axis). The activity level values may be determined using EQUATIONS 2 and/or 3. Curve 402 may be produced using one of EQUATIONS 2 and 3 where a first value for the decay coefficient “r” is selected for ST usage. Curve 404 may be produced using one of EQUATIONS 2 and 3 where a second value for the decay coefficient “r” is selected for LT usage. The values selected for “r” in connection with 402 and 404 may be relative so that the first value for “r” used with 402 is less than the second value for “r” used with 404.

In one embodiment, each of the different An values determined using EQUATION 2 may be converted to a corresponding Ar value using EQUATION 3 when desired.

In connection with the foregoing, for example, with respect to a number of read misses, “a_(n)” represents the number of such operations that have occurred in a current sample period, n. For example, if a sample period=10 minutes so that statistics for an extent are collected and/or computed every 10 minutes, “a_(n)” represents the number of read misses that occurred in the last 10 minute sample period or time interval. A_(n-1) represents the previous or last A calculation (e.g., as determined using EQUATION 2) from the previous sample period, denoted “n−1”.

With reference back to FIG. 10, an embodiment may collect short term information 302 as counter values indicating a count or number of each type of operation for a current time period or sampling period “n”. The following may represent different “a_(n)” values as included in the short term information 302 for an extent: read miss count (number of read misses for the extent during the sampling period), pre-fetch count (number of pre-fetches for the extent during the sampling period) and write count (number of writes for the extent during the sampling period).

The short term information 302 may also include storing previous A values as determined for the sampling period “n−1” using EQUATION 2 above. For example, short term information 302 may also include storing three (3) previous adjusted activity level values or A values for sampling period “n−1” using EQUATION 2 above for the read miss count, pre-fetch count and write count.

The short term information 302 may also include a timestamp value indicating the timestamp associated with the previous sampling period “n−1”.

Using the above-mentioned short term information 302, an embodiment may calculate updated short term rates 320 using EQUATION 3 for a sampling period “n” for a selected “r” as a short term decay coefficient. With each new sampling period, the short term information may be accordingly updated so that which is associated with sampling period “n” subsequently becomes associated with sampling period “n−1”.

The long term information 304 may include long term rates or Ar values as determined using EQUATION 3 for a read miss rate (e.g., number of read misses/second), a pre-fetch rate (e.g., number of pre-fetches/second) and a write rate (e.g., number of writes/second). The long term information 304 may also include a time duration interval used for determining an adjusted Ar value for the current time or sampling period “n”. For example, the time duration interval may represent the amount of time for which statistics are collected and used in connection with long term Ar values. An embodiment may store a set of long term Ar values rather than calculate such Ar values on demand from other stored information as in the case above for short term rates 320 (e.g., where short term information 302 is stored and used to calculate short term rates 320 on demand). Thus, in such an embodiment, the long term rates 330 may be included the long term information 304 where such long term rates 330 may be updated with each sampling period. In one embodiment with the arrival of a new sampling period “n”, the long term information 304 may include Ar values for the foregoing statistics as determined using EQUATION 3 for a sampling period “n−1”. These long term Ar values for “n−1” may each be multiplied by the time duration interval to determine A_(n-1), an adjusted metric for the long term time period. The foregoing A_(n-1) value may then be used with EQUATION 2 to determine An for the current sampling period “n” using a selected “r” as a long term decay coefficient. Using An, EQUATION 3 may then be used to obtain updated long term rates Ar values. With each new sampling period, the long term information may be accordingly updated so that which is associated with sampling period “n” subsequently becomes associated with sampling period “n−1”.

With reference back to FIG. 10, described above is an activity bitmap 306 having an entry per sub extent where each such entry may indicate an aggregate or collective activity level with respect to all chunks of the associated sub-extent. The number of different activity level states that may be represented for each sub extent depends on the number of bits per entry of the activity bitmap. In one embodiment, each entry of the activity bitmap may be 2 bits as described above so that each entry may be an integer in the inclusive range of 0 . . . 3. Processing may be performed to decrement each entry having a non-zero value by 1 every predetermined time period, such as every 12 hours. Each time there is any I/O operation to a sub extent since the sub extent was located or moved to its current physical location, the sub extent's entry in the activity bitmap 306 may be set to 3. Thus, each entry in the bitmap may represent activity level information for up to 3 of the predetermined 12 hour time periods. An embodiment may also have a different number of bits per entry to represent a larger number of predetermined time periods. Based on the foregoing, the lower the value of a bitmap entry for a sub extent, the longer the amount of time that has lapsed since the sub extent has had any I/O activity.

Referring to FIG. 12, shown is a flowchart of processing steps that may be performed in connection with each activity bitmap associated with an extent in an embodiment in accordance with techniques herein. The flowchart 500 summarizes processing described above where each bitmap for each extent may be traversed with the occurrence of a predetermined time interval, such as every 12 hours. At step 502, a determination is made as to whether the next time interval has lapsed. If not, processing waits at step 502 until step 502 evaluates to yes and control proceeds to step 504. At step 504, I is initialized to the next entry in the bitmap. I represents a loop counter when traversing through the bitmap and denotes the bitmap entry currently selected for processing. At step 506, a determination is made as to whether the entire bitmap has been processed. If step 506 evaluates to yes, control proceeds to step 502 until an amount of time again lapses equal to that of the time interval. If step 506 evaluates to no, control proceeds to step 508 where a determination is made as to whether the current bitmap entry (e.g., bitmap [I]) is zero. If so, control proceeds to step 504. Otherwise, control proceeds to step 510 where the current bit map entry is decremented by one (1) and control proceeds to step 504 to process the next entry in the bitmap.

The activity bitmap may be used in connection with determining an activity level associated with each sub extent, the smallest amount of data that can be associated with a data movement operation to relocate data from one physical device to another. It should be noted that an embodiment may have functionality and capability to physically move data in units or amounts less than a sub extent. However, when performing processing to determine data movement candidates, such as by the optimizer, such processing may consider candidates for data movement which have a minimum size of a sub extent. That is, all data of the sub extent may be either moved or relocated as a complete unit, or remains in its current location. In connection with a sub extent when performing a data movement, it may be that not all chunks of the sub extent are actually moved. For example, suppose a sub extent is 10 chunks and the sub extent is to be moved from a first storage tier, such as from low-speed or high-speed drives, to a second storage tier, such as flash. It may be that 9/10 chunks of the sub extent are unallocated or already in flash storage with only 1 chunk stored in the first storage tier. In this case, processing only needs to actually move the single chunk from the first storage tier to flash since the remaining 9 chunks are either already in the flash tier or unallocated. With a sub extent, the amount of data actually moved may be at most the size of the sub extent but may be less depending on, for example, whether all chunks of the thin device sub extent are allocated (e.g., actually map to physical storage), depending on the current physical device upon which chunks of the sub extent are located prior to movement, and the like. It should be noted that chunks of a sub extent may be located in different storage tiers, for example, depending on where the chunk's data is stored such as at the time when written as well as the result of other conditions that may vary with embodiment.

As an example use of the activity bitmap is in connection with promotion and demotion. As an example use of the activity bitmap, the bitmap may be used to determine selective sub extents which exhibit the highest activity level such as those having counters=3 (e.g., “hot” or active areas of the extent). These sub extents may be candidates for promotion or data movement to a higher performing storage tier and may be given preference for such promotion and data movement over other sub extents having activity bitmap entries which are less than 3. In a similar manner, the activity bitmap may be used to identify the “coldest” or inactive sub extents. For example, sub extents having bit map entries=0 may be candidates for demotion to a lower performing storage tier.

In connection with promotion data movements, an embodiment may want to be responsive to a change in workload with respect to the short term. With demotion, an embodiment may not want to move data as quickly as with promotion and may also want to consider longer term workloads prior to moving such data to a lesser performing storage tier. With promotion, an embodiment may give greater weight to ST workload and activity data. With demotion, an embodiment may additionally consider LT workload and activity rather than just such ST information.

The information as described and illustrated in FIGS. 10-12 above may be used for a variety of different purposes and evaluations. For example, an embodiment may use one or more of the short term rates to identify one or more active extents based on such aggregated extent-level activity data. Subsequently, once an active extent is identified such as a candidate for promotion, the extent's activity bitmap may be examined to determine which sub extents are most active. Processing may be performed to selectively move some of the sub extents of the active extent (e.g., those with counters=3) to a higher performing storage tier.

As another example, the activity bitmaps of extents may be used to determine a promotion ranking used to identify which extent may be promoted prior to one or more other extents. To further illustrate, an embodiment may have two extents, both which are candidates for promotion. The two extents may exhibit similar activity levels based on aggregate extent-level information such as based on short term rates 320 for each extent. The extent having the lesser number of active sub extents may have a higher priority for movement than the other extent. For example, processing may be performed to count the number of non-zero bit map entries for each of the two extents. The extent having the lower count may have a higher priority than the other extent having a higher count. In other words, the extents may be ranked or ordered for promotion based on a number or count of non-zero bit map entries. The extent having the lower count may be characterized as also exhibiting the greatest activity level density based on the foregoing counts of the activity bitmaps.

As another example in connection with demotion, an embodiment may use one or more of the short term rates 320 in combination with one or more of the long term rates 330 to identify one or more inactive extents based on such aggregated extent-level activity data. Subsequently, once an inactive extent is identified, the extent's activity bitmap may be examined to determine which sub extents are inactive and should be demoted rather than automatically demoting all sub extents of the inactive extent. Processing may be performed to selectively move some of the sub extents (e.g., those with counters=0, counters less than some threshold such as 1, and the like) to a lower performing storage tier.

One embodiment in accordance with techniques herein may include multiple storage tiers including a first tier of flash devices and one or more other tiers of non-flash devices having lower performance characteristics than flash devices. The one or more other tiers may include, for example, one or more types of disk devices. The tiers may also include other types of SSDs besides flash devices.

The different levels of activity information described herein as obtained at a thin device level, extent level, and sub extent level provide a hierarchical view for characterizing activity of different portions of thin devices. Activity information at higher device levels may be used to first identify devices which may be candidates for data movement, such as between storage tiers (e.g. for promotion and/or demotion). In connection with thin devices, once such a first device is identified, additional detail regarding the first device's activity as reflected in extent activity level information may be used to identify an extent of the first device as a candidate for data movement. Subsequently, the activity bitmap for the extent identified may then be used to determine one or more sub extents of the identified extent for data movement. The techniques herein may be used for collecting and tracking activity of thin devices. Use of the decay coefficients and equations for determining adjusted activity levels to account for previous activity levels provides an effective way of tracking workload and activity over time without having to keep a large database of historical statistics and metrics for long and short time periods.

In addition to the activity information described above for each extent and sub extent of a thin device, an embodiment may also track device level activity information for logical devices (e.g., thin devices, LVs, and the like) and PSUs in a data storage system as also noted. Additionally, an embodiment may track activity information for thin device pools. When a DA or other device interface services an I/O, the DA may not typically have any knowledge regarding thin devices as may be known from the host's point of view. In connection with collecting data for use with techniques herein, each DA may be provided with additional mapping information regarding thin devices and where storage for the thin devices is allocated (e.g., such as described by the allocation map). The DA may use this information to determine what thin device (if any) is associated with a given back-end I/O request. When the DA is servicing a back-end I/O request, the DA may record information about the I/O including information about the thin device associated with the I/O request. Such additional information about the thin device may be used in order to perform statistics collection of activity data for the thin devices in accordance with techniques herein.

In addition to the statistics and activity data described above, an embodiment may also collect and store information regarding expected I/O size information for each extent, thin device (or other logical device), physical device, and the like. Such information may be determined in any one or more suitable ways in an embodiment. For example, an embodiment may determine expected I/O sizes that represent the average size with respect each of the particular types of I/O operations for which statistics are collected. In connection with the embodiment herein, the types of I/O operations for which statistics are collected may be as described above for read miss or random read miss (RRM), pre-fetch (P) or sequential read miss (SRM), and write (W). In a manner similar to that as described elsewhere herein for other statistics, the average I/O sizes may be determined based on size information collected for observed I/O operations. The collected size information based on observed I/Os may be used in determining or modeling expected I/O sizes in connection with equations, such as EQUATION 4, described elsewhere herein when determining various scores. For example, an embodiment may determine a first average I/O size based on I/O sizes of write operations observed for a time period, a second average I/O size based on I/O sizes for SRM operations for a time period, and a third average I/O size based on I/O sizes for RRM operations for a time period. The foregoing average I/O sizes may be tracked with respect to each extent and other levels (e.g., thin device, physical device, etc.) in a manner similar to that as described above such as in FIG. 10 for other statistics. An embodiment may also use other approaches which may be further simplified. For example, rather than track such I/O size information for each extent, an embodiment may determine an average I/O size with respect to each particular type of I/O operation (W, RRM and SRM) as an aggregate across one or more devices, such as for a physical device, pool of PSUs, thin device, and the like, and then determine an average I/O size with respect to all extents or data portions thereof. In one embodiment, the expected I/O size for any desired I/O operation type such as used in connection with EQUATIONs 4 and 5 described elsewhere herein, may be computed as an average I/O size based on previously gathered data including metrics related to total amount of data (in bytes, megabytes, or other size unit) for a given time period and total number of I/O operations (for the time period over which the total amount of data is determined). More formally, the average I/O size used as an expected I/O size for a given I/O type may be represented as: Ave size for given I/O type=TOTAL_DATA_TRANSFER/TOTAL_OPS  EQUATION 3A where

“Ave size for given I/O type” is the average or expected I/O size for a given I/O operation type (e.g., Read, Write, Read miss, etc.);

“TOTAL_DATA_TRANSFER” is the total amount of data (e.g., in bytes, megabytes or other size unit) for the desired I/O operation type for a given time period; and

“TOTAL_OPS” is the total number of I/O operations observed during the time period for which the TOTAL_DATA_TRANSFER is observed.

It should be noted that EQUATION 3A is one way in which an embodiment may estimate that averages as may be used in connection with expected I/O sizes as described elsewhere herein. Another way an embodiment may determine average I/O sizes is based on a an equation using weighted averages, using information as may be gathered using the allocation map as described elsewhere herein (e.g., to gather information for data portions based on I/Os directed to the physical device where such data portions are stored), and more generally any suitable technique.

In connection with techniques in following paragraphs, the extent-based short term and long term statistics or metrics as described in FIG. 10 may be used in determining scores indicating the activity of extents. In one embodiment, the score may be a weighted value based on a combination of all six metrics 322, 324, 326, 332, 334 and 336 of FIG. 10 although an embodiment may generally use any metrics in determining such scores. In an embodiment herein, a promotion score for an extent may be represented in EQUATION 4 as: ((P1*P7*s_rrm)+(P2*P8*s_w)+(P3*P9*s_p)+(P4*P10*l_rrm)+(P5*P11*l_w)+(P6*P12*l_p))/(#Active Subext+1) where s_rrm is the rate of short term random read misses (322), s_w is the rate of short term writes (324), s_p is the rate of short term pre-fetches or SRMs (326), l_rrm is the rate of long term random read misses (332), l_w is the rate of long term writes (334), and l_p is the rate of long term pre-fetches or SRMs. The coefficients P1-P12 may be set as appropriate and are described in more detail elsewhere herein. It should be noted that “#Active Subext” represents the number of active subextents or subportions of an extent or other larger data portion for which the score is being determined. Examples of evaluating when a subextent or other subportion is active are described elsewhere herein. It should be noted that metrics used in connection with determining promotion and/or demotion score may take into account I/O size.

The coefficients P1-P6 may represent weights assigned to the different operation types denoting how much weight is given to each particular operation type (e.g., which of random read miss (RRM), pre-fetch (P) or sequential read miss (SRM), write (W)) and the long term and short term variants of expected rates at which such operation types are expected (e.g., predicted or modeled) to occur in the future. In one aspect, the coefficients P1 and P4 represent the weighted preference given to the RRM operation type relative to the other operations types of SRM (or P) and W. In particular, P1 represents the weighted preference given to the short term operation count or rate for the RRM operation type and P4 represents the weighted preference given to the long term operation count or rate for the RRM operation type. In a similar manner, the coefficients P2 and P5 represent the weighted preference given to the W operation type relative to the other operations types of SRM (or P) and RRM. In particular, P2 represents the weighted preference given to the short term operation count or rate for the W operation type and P5 represents the weighted preference given to the long term operation count or rate for the W operation type. Furthermore, the coefficients P3 and P6 represent the weighted preference given to the P or SRM operation type relative to the other operations types of W and RRM. In particular, P3 represents the weighted preference given to the short term operation count or rate for the P or SRM operation type and P6 represents the weighted preference given to the long term operation count or rate for the P or SRM operation type. The weights or coefficients P1-P6 may be generally referred to as operation type weights. In some embodiments, values for P1-P6 may be dynamically selected each time a new set of statistics or metrics (e.g., 320 and 330 of FIG. 10) are utilized in performing processing described herein. Values for P1-P6 may be generally selected based on expected storage tier workload characteristics and particular performance characteristics of PSUs in the different tiers. Examples of how values for P1-P6 may be selected are described in more detail elsewhere herein. It should be noted that an embodiment may also use a combination of fixed values for P1-P6 when determining a score in connection with evaluating which data portions to store in one or more of the storage tiers and may use dynamically determined values for P1-P6 when determining a score in connection with evaluating which data portions to store in one or more others of the storage tiers. For example, an embodiment may use dynamically selected values for P1-P6 when determining a promotion score of EQUATION 4 for use when evaluating which data portions to store in a target high performing SSD or flash-based storage tier, and may otherwise use a same set of fixed values for P1-P6 when determining a promotion score of EQUATION 4 for use when evaluating which data portions to store in a non-SSD or non-flash-based storage tiers (e.g., storage tiers comprising rotational disk drives). In an embodiment, the fixed values used for P1-P6 for non-SSD-based tiers may be 12, 4, 4, 3, 1, and 1, respectively. Of course, different values may be used to emphasize or deemphasize different I/O characteristics in connection with determination of the promotion raw score. Thus, different values for weights P1-P6 may be selected for use depending on which target tier the promotion score is being calculated for. Such values may be dynamically and continually determined based on current expected workload characteristics of a storage tier at different points in time. An embodiment may also selected weights for P1-P6 which are fixed or static throughout operation and performance of the techniques herein where such a fixed set of the same weights may be used for one or more storage tiers.

The coefficients P7-P12 may represent additional weights assigned or associated with each particular variant combination of operation type (e.g., RRM, SRM or P, and W) and short term or long term for each operation type. Generally, the coefficients P7-P12 may represent weighting factors that may be characterized as varying with, dependent on, or a function of, expected I/O size for the three different operation types of RRM, SRM or P, and W. In particular, P7 and P10 represent weighting factors that vary with, or are a function of, expected I/O size for the RRM operation type. P8 and P11 represent weighting factors that vary with, or are a function of, expected I/O size for the W operation type. P9 and P12 represent weighting factors that vary with, or are a function of, expected I/O size for the P or SRM operation type. Weights P7-P12 may also be referred to herein as I/O size or data transfer weights. As noted above, EQUATION 3A is one way in which the expected I/O size may be determined for use in connection with determining such weights. It should also be noted that as a variation to the above where in one embodiment, size weights as represented using P7-P12 may be applied to only the short term metrics (e.g., always use a size weight of 1 for weights P10, P11 and P12 for long term metrics).

In some embodiments, values for P7-P12 may be dynamically selected each time a new set of statistics or metrics (e.g., 320 and 330 of FIG. 10) are utilized in performing processing described herein. Values for P7-P12 may be generally selected based on expected storage tier workload characteristics and particular performance characteristics of PSUs in the different tiers. For example, as described in more detail elsewhere herein, if particular storage tiers have PSUs where a response time or other measurement of performance does not exhibit a substantial dependency upon I/O size, then values for P7-P12 may be 1 so as not to introduce any bias based upon expected I/O sizes for the different operation types. Examples of how values for P7-P12 may be selected are described in more detail elsewhere herein. It should be noted that an embodiment may also use fixed values for P7-P12 when determining a score in connection with evaluating which data portions to store in one or more of the storage tiers and may use dynamically determined values for P7-P12 when determining a score in connection with evaluating which data portions to store in one or more others of the storage tiers. For example, an embodiment may use dynamically selected values for P7-P12 when determining a promotion score of EQUATION 4 for use when evaluating which data portions to store in a target high performing SSD or flash-based storage tier and may otherwise use a set of fixed values for P7-P12 of 1 for all of P7-P12 when determining a promotion score of EQUATION 4 for use when evaluating which data portions to store in a non-SSD or non-flash-based storage tiers (e.g., storage tiers comprising rotational disk drives). Of course, different values may be used to emphasize or deemphasize different I/O characteristics in connection with determination of the promotion raw score. Thus, different values for weights P7-P12 may be selected for use depending on which target tier the promotion score is being calculated for.

Values of P7-P12 may be selected as a function of expected I/O sizes for the different operation types. For example, P7 and P10 may be determined as a function of the expected I/O size of the RRM operations with respect to the extents for which the promotion score is being determined. P8 and P11 may be determined as a function of the expected I/O size of the W operations with respect to the extents for which the promotion score is being determined. P9 and P12 may be determined as a function of the expected I/O size of the SRM or P operations with respect to the extents for which the promotion score is being determined.

Values for P7-P12 may be based on each storage tier and drive technology depending on the sensitivity of response time to I/O size. Thus, the drive technology may be used in selecting that particular values for P7-P12 such as using curves of FIGS. 13D and 13E where the more sensitive or greater dependency between response time and I/O size, the greater the variation in values of the bias or weights assigned.

The demotion score for an extent may be represented in EQUATION 5 as: (P4*P10*s_rrm)+(P5*P11*s_w)+(P6*P12*s_p)+(P1*P7*l_rrm)+(P2*P8*l_w)+(P3*P9*l_p) where s_rrm, s_w, p1, etc. are as set forth above.

As noted above in connection with the exemplary EQUATIONS 4 and 5 for computing, respectively, the promotion and demotion scores, the same set of coefficients may be used. Alternatively, an embodiment may, however, use a different set of coefficients for computing the promotion and demotion scores.

In a multi-tiered data storage system as described herein, an application having its data stored on thin devices of a storage group may be allowed to use multiple tiers of storage. In order to be able to use the storage of the tiers efficiently and also move a minimal number of chunks between tiers, chunks which are the most active or “hot” need to be located in the higher tiers (e.g., promoted to such tiers if not already located there) and chunks which are least active or “cold” need to be located in lower storage tiers (e.g., demoted to such tiers if not already located there). After identifying the hot and cold chunks, processing may be performed to determine how much of the hot chunks should be placed in the different storage tiers in order to efficiently utilize the higher performing tiers, such as flash tiers, while also avoiding overloading any given tier with I/O request or I/O transfer activity to the point that overall performance (e.g., across all tiers in the AP, across one or more SGs, for the whole data storage system, and the like with respect to the PSUs under consideration) would have been better had less of the workload been placed in the tier. In connection with the foregoing, techniques are described in following paragraphs which determine promotion and demotion thresholds of a data movement policy that may be associated with one or more SGs. The data movement policy as described herein in the context of thin devices affects what data portions of thin devices are data movement candidates and may be moved to another tier. The selection of promotion and demotion thresholds may be made by considering criteria including performance limits (e.g., response time, number of I/Os per time period, and the like) and capacity limits. The performance limits may be flexible or adaptable and specified for each storage tier. The capacity limits may also be specified for each storage tier and may include capacity limits included in an AP for the affected one or more SGs. The techniques model response time of target storage tiers when evaluating different alternative hypothetical considerations in which performance limits are varied for each tier when selecting promotion and demotion thresholds. The different sets of performance limits in combination with capacity limits are evaluated by modeling the expected target tier performance and then determining an overall performance metric representing an aggregate modeled performance metric across all target storage tiers for all affected SGs. In one embodiment, the overall performance metric may be an average response time determined with respect to all target storage tiers using the modeled response time as determined for each such tier. The average response time is used to compare the overall modeled performance for the storage tiers when evaluating different sets of performance limits for each target tier. Each set of performance limits specified for multiple tiers may be used as a way to provide weighting factors for I/O workload distribution across the tiers in order to reflect the performance differences of the different tier storage technologies. Utilizing such “what if” analysis to evaluate different sets of performance limits coupled with capacity limits provides for determining promotion and demotion thresholds that may be used by the DA, or more generally, other backend data storage system components, in connection with performing data movements in accordance with workload or performance impact across all target storage tiers to increase overall performance.

In connection with techniques herein as mentioned above, response time may be considered as performance criteria alone, or in combination with other performance criteria in combination with capacity limits, when determining promotion and demotion thresholds affected what data portions of a thin device may be moved between PSUs in different storage tiers. The techniques herein consider different performance characteristic information and curves that may vary with each storage tier, type of physical device, device vendor, and the like. In particular, performance curves for the different storage tiers may be determined and used to model target tier and also overall SG performance across storage tiers as part of processing to evaluate different sets of performance limits in combination with capacity limits. As an example, consider a workload of N I/O operations/second. The response time experienced for the same workload varies with storage tier due to the underlying capabilities of each tier's technology. As such, performance curves may be used in connection with techniques herein to model expected response times if a particular data movement is performed in accordance with candidate promotion and demotion thresholds.

FIG. 13 is an example of a graph 1300 representing levels of compressibility and I/O activity in accordance with some embodiments of the invention. Graph 1300 is merely an illustrative embodiment of levels of compressibility and I/O activity in accordance with some embodiments of the invention. Any of numerous other implementations of levels of compressibility and I/O activity, for example, variations of the levels illustrated in graph 1300, are possible and are intended to fall within the scope of the invention. For example, although three ranges and levels of I/O activity and compressibility are illustrated in graph 1300, and described in relation to some embodiments of the invention, any number of ranges and/or levels of such parameters may be used, for example, two, or four or more.

The x-axis 1304 represents I/O activity of a VSU, and the y-axis 1302 represents compressibility of a VSU. Along the x-axis: a low I/O activity range 1320 is defined between the origin and low I/O activity threshold 1316; a moderate I/O activity range 1322 is defined between the low I/O activity threshold 1316 and the high I/O activity threshold 1318; and a high I/O activity range 1324 is defined the right of the high I/O activity threshold 1318. For example, the values of thresholds 1316 and 1318 may be 50% and 80% of a maximum I/O activity value, such that low, moderate and high I/O activity ranges 1320, 1322 and 1324 are: 0-50%, 50-80% and 80-100%, respectively. I/O activity may be measured, and thus thresholds, ranges and levels defined, using any of a plurality of metrics and units, for example, I/O density—e.g., (I/O operations per second)/(GB of storage), a value indicative of percentage of overall I/O activity on a storage system, or any of the metrics or units discussed above in relation to FAST. It should be appreciated that any desirable threshold values may be defined, any desirable number of I/O activity ranges (e.g., two, four or more) may be defined, and any desirable I/O activity metrics or units of measure may be used; and each of such values may be configured into compression decision logic. I/O activity levels (e.g., high, moderate and low) may be defined that represent each I/O activity range 1320, 1322 and 1324, respectively.

Compression decision logic, compression scanning logic and other logic described herein, and methods 1400 and 1600, described below, and acts or parts thereof, may be implemented using one or more system components described in relation to FIGS. 1-3, including service processor 22, data services component 24, performance data monitoring software 134 and/or optimizer 128.

Along the y-axis: a low compressibility range 1310 is defined between the origin and low compressibility threshold 1306; a moderate compressibility range 1312 is defined between the low compressibility threshold 1306 and the high compressibility threshold 1308; and a high compressibility range 1314 is defined above the high I/O compressibility threshold 1308. For example, the values of thresholds 1306 and 1308 may be expressed as ratios, and may be equal to 2:1 (i.e., 2) and 3:1 (i.e., 3), respectively, such that low, moderate and high compressibility ranges 1310, 1312 and 1314 are: 0-2, 2-3 and >3 respectively. It should be appreciated that any desirable threshold values may be defined, any desirable number of compressibility ranges (e.g., two, four or more) may be defined, and any desirable compressibility units of measure may be used; and each of such values may be configured into compression decision logic. Compressibility levels (e.g., high, moderate and low) may be defined that represent each compressibility range 1310, 1312 and 1314, respectively.

Each combination of compressibility range and I/O activity range may correspond to a region of graph 1300, including 1326, 1328, 1330, 1332, 1334, 1336, 1338, 1340 and 1342.

Compression decision rules for VSUs may be defined based at least in part on I/O activity of the VSU, compressibility of the VSU and system capacity utilization, for example, on I/O activity levels (e.g., defined as I/O activity ranges), compressibility levels (e.g., defined as compressibility value ranges) and system capacity utilization levels (e.g., defined as system capacity utilization ranges). Table 1 illustrates an example of compression decision rules, which may be implemented in compression decision logic, represented by values in a data structure, or a combination thereof. Table 1 is merely an illustrative embodiment of compression decision rules in accordance with some embodiments of the invention. Any of numerous other implementations of compression decision rules, for example, variations of the rules illustrated in Table 1, are possible and are intended to fall within the scope of the invention. For example, any number of levels, less than or greater than three) may be defined for each compression decision parameter represented in Table 1, and rules defined according to same. Further, any of numerous other factors may be employed, perhaps in combination with the compression decision parameters described below, to make compression decisions, such as, for example: FAST tier, Service Level Objectives (SLOs), performance objectives, workload type, PSD type, performance or utilization measures (e.g., any of those describe above in relation to FAST), other factors, or any suitable combination of the foregoing. For example, any of the performance objective levels, workload types, device types of other suitable factors described in U.S. patent application Ser. No. 14/586,497, filed Dec. 30, 2014, “Application-Specific Workload-Based I/O Performance Management” by Aharoni, et al., which is hereby incorporated by reference in its entirety, may be defined as part of compression decision rules or used as part of compression decision logic.

Each of the first three columns of Table 1 represent a compression decision parameter, and the fourth column represents a decision based on compression decision parameter values of the previous three columns. The value of each compression decision parameter may be one of a predefined set of values, for example, high, moderate or low. For example, the values of the I/O activity level and/or compressibility level may correspond to a range of I/O activity values and compressibility values, respectively, as described above in relation to FIG. 13. The predefined set of potential values of system capacity utilization levels, e.g., low, moderate and high, may correspond to a range of system capacity utilization values. For example, low, moderate and high capacity utilization values may correspond to ranges of: 0-50%, 50%-80% and >80%, respectively. It should be appreciated that any desirable number of capacity utilization ranges (and levels) may be used and may be configured into compression decision rules and logic.

TABLE 1 Compression decision rules Capacity I/O Activity Compressibility Row # Utilization Level Level Level Compress? 1 High High, Moderate, High, Moderate, Yes Low Low 2 Moderate High High Yes 3 Moderate High Moderate, Low No 4 Moderate Moderate, Low High, Moderate, Yes Low 5 Low High High, Moderate, No Low 6 Low Moderate High, Moderate Yes 7 Low Moderate Low No 8 Low Low High, Moderate, Yes Low

For example, per Row 1, if a system capacity utilization level is high, a VSU should be compressed regardless of the I/O activity level or the compressibility level of the VSU. Per the combination of Rows 1, 4 and 8, if the I/O activity level of a VSU is low (e.g., range 1320 in FIG. 13), the VUS data should be compressed irrespective of system capacity utilization level or compressibility level of the VSU. That is, for the region represented by 1327 in FIG. 13, VSUs will be compressed regardless of system capacity utilization. Per the combination of Rows 1, 3 and 5, for VSUs having high activity levels and moderate or low compressibility levels (e.g., corresponding to region 1331 in FIG. 13), data will only be compressed if system capacity utilization is high.

FIG. 14 is a flowchart illustrating an example of a method 1400 of intelligently compressing virtual storage unit data in accordance with some embodiments of the invention. Method 1400 is merely an illustrative embodiment of a method of intelligently compressing virtual storage unit data. Any of numerous other implementations of levels of such a method, for example, variations of method 1400, are possible and are intended to fall within the scope of the invention.

In act 1402, a write I/O request for first data of a VSU may be received (e.g., at an HA 21 of storage system 12). In act 1404, it may be determined whether the write I/O request is an initial write request for the VSU, i.e., a new allocation—a first-ever write to a physical storage address range represented by the VSU. If the write request is determined to be an initial write request for the VSU, then, in act 1406, the first data may be compressed and stored at a physical media location corresponding to the VSU (perhaps after first being staged in cache), e.g., irrespective of any capacity utilization value of the storage system. Further, it should be appreciated that, for an initial write request for a VSU, there is no I/O activity history yet, as this is the first-ever I/O operation for the VSU, so method 1400 may be configure to not consider I/O activity for an initial write I/O request.

In act 1414, a compressibility value for the VSU may be updated. For example, as it is the initial write operation of the VSU, the compressibility value may be calculated as the compression ratio of the first data. The compressibility value, compressibility level corresponding to the compressibility value (e.g., as described above in relation to FIG. 13 and Table 1) and the time at which act 1414 was performed, may be recorded in one or more data structures of the storage system, for example, any described above in relation to FAST, or in fields 1516, 1518 and 1520 of data structure 1500, as described below in relation to FIG. 15.

FIG. 15 illustrates an example of a data structure 1500 for compression decision data in accordance with some embodiments of the invention. Data structure 1500 is merely an illustrative embodiment of a data structure 1500 for compression decision data. Any of numerous other implementations of a data structure for compression decision data, for example, variations of data structure 1500, are possible and are intended to fall within the scope of the invention.

Data structure 1500 may include a plurality of data of entries, 1502-1508, each entry representing a VSU. Each entry may have a value for one or more of the following fields: VSU ID 1510; I/O activity 1512; I/O activity level 1514, compressibility value 1516, compressibility level 1518, compressibility last updated 1520 and one or more other fields 1522. VSU ID field 1510 may store a unique ID for a VSU, which may serve as a key to an entry in data structure 1500. I/O activity field 1512 may hold an I/O activity value for the VSU; and I/O activity level field 1514 may hold the activity level associated with the I/O activity value, for example, in accordance with the ranges described above in relation to FIG. 13 and Table 1. Compressibility value field 1516 may hold a compressibility value for the VSU; and compressibility level field 1518 may hold the compressibility level associated with the compressibility value, for example, in accordance with the ranges described above in relation to FIG. 13 and Table 1. These fields may be populated in accordance with performance of acts 1406 or 1412 of method 1400 described above, or in accordance with performance of method 1600 or other processes associated with any of the values stored, e.g., FAST processes.

Returning to act 1404 of method 1400, if it is determined that the write I/O request is not the initial write request, a decision may be made whether to compress the data based on: a system capacity utilization of the storage system; and I/O activity of the first VSU; and/or compressibility of the first VSU. For example, such decision may be based on the decision rules described above in relation to Table 1 or other decision rules. If it is determined to compress the first data, then, in act 1410, the data is compressed and stored at a physical media location corresponding to the VSU (perhaps after first being staged in cache).

In act 1412, it may be determined whether to update the compressibility value, for example, in accordance with preconfigured logic. It should be appreciated that the decision of whether to update the compressibility value of a VSU is a separate decision from whether to compress VSU data, and each decision does not necessarily correlate with the other. That is, it may be determined to compress the VSU data, but not update the compressibility value of the VSU; and, conversely, it may be determined to not compress the VSU data (e.g., in act 1408), but to update the compressibility value (e.g., in act 1412). If should also be appreciated that compressibility values and levels of VSUs, I/O activity values and levels of VSUs and/or system capacity utilization values and levels of VSUs may be updated as a part of processes independent from methods 1400 and 1600 described below, for example, as part of FAST data collection, aggregation and calculations processes described above in relation to FIGS. 4-12. Further, various acts and portions thereof described in relation to methods 1400 or 1600 and FIGS. 13-16 may be integrated into FAST processes described above, and one or more elements of FAST processes may be integrated into either of methods 1400 or 1600.

If it is determined in act 1412 to update the compressibility value, then, in act 1414, the compressibility value may be updated as described above, and stored in a FAST data structure and/or data structure 1500. Further, in some embodiments, the history of compressibility values for a VSU is considered (e.g., by accessing the historical values in a data structure), and the compressibility level may be determined based at least in part on such history. For example, if there is a large degree of volatility historically in the compressibility value determined for a VSU, a compressibility level may be assigned that is greater than the level associated with the determined compressibility value. For example, even if the determined compressibility value falls within a predefined low or moderate compressibility range, a determined level of volatility above a certain threshold may result in assigning a high or moderate compressibility level, respectively, to the VSU. Any suitable combination of statistical analyses may be used to determine volatility, for example, standard deviation, e.g., in combination with one or more other statistical functions.

It should be appreciated that method 1400 may include additional acts. Further, while the acts of method 1400 are illustrated in FIG. 14 as being performed serially, the invention is not so limited, and one or more of the acts, or parts thereof, may be performed concurrently, and two or more of the acts may performed in different orders than illustrated in FIG. 14. For example, the decisions of whether to compress VSU data and whether to update a compressibility value may be performed in different orders than shown in FIG. 14 and/or concurrently (at least in part).

FIG. 16 is a flowchart illustrating an example of a method 1600 of determining whether to compress data of a virtual storage unit in accordance with some embodiments of the invention. Method 1600 is merely an illustrative embodiment of determining whether to compress data of a virtual storage unit. Any of numerous other implementations of levels of such a method, for example, variations of method 1600, are possible and are intended to fall within the scope of the invention.

Method 1600, or parts thereof, may be executed as part of a compression scanning process and/or as part of act 1408 in response to receiving a write I/O request. Method 1600 may be performed: periodically; in response to user input; in response to a detected change in compression decision parameter level; and/or in response to another system event. Further method 1600 may be performed continually, and may be performed as a background daemon on a storage system.

In act 1604, the capacity utilization level of the storage system or portion thereof may be determined, for example, from one of more data structures (e.g., FAST data structures) resident on the system. If the capacity utilization level is determined to be low, then method 1600 may be configured to not perform any other steps of method 1600, and not compress any uncompressed VSU data. Such configuration may be desirable to avoid unnecessary use of system CPU and bandwidth resources during a time in which capacity utilization is low, and thus storage capacity is not as scarce. In such a case, method 1600 may continuously return to act 1602 if running in continuous mode, or otherwise end if configured to run in response to some sort of event or input, as illustrated by arrow 1603.

If it is determined in act 1604 that the capacity utilization level is not low, then, in act 1606, a next VSU to be considered may be determined, for example, based on compression scanning process rules. The next VSU may be determined in any of a variety of ways, and may depend at least in part on the event or input that triggered execution of method 1600. For example, in some embodiments, method 1600 may be configured to only consider uncompressed VSUs, as it may be considered a poor use of system resources to decompress compressed data. On the other hand, it may be desirable to decompress data when system capacity utilization is moderate or low, especially if it is determined to be a period of low resource utilization (e.g., system wide)(not shown)—to avoid future I/O latency and/or resource consumption during a time of high resource utilization.

In some embodiments, a next VSU (e.g., a next uncompressed VSU) may be selected in accordance with a predefined order based on I/O activity and/or compressibility, e.g., accordingly to the following order based on VSU compression decision parameter values:

1. Low I/O activity level:

-   -   a. high compressibility level (e.g., region 1338 in FIG. 13);     -   b. moderate compressibility level (e.g., region 1332 in FIG.         13);     -   c. low compressibility level (e.g., region 1326 in FIG. 13);

2. Moderate I/O activity level:

-   -   a. high compressibility level (e.g., region 1340 in FIG. 13);     -   b. moderate compressibility level (e.g., region 1334 in FIG.         13);     -   c. low compressibility level (e.g., region 1328 in FIG. 13);

3. High I/O activity level:

-   -   a. high compressibility level (e.g., region 1342 in FIG. 13);     -   b. moderate compressibility level (e.g., region 1336 in FIG.         13);     -   c. low compressibility level (e.g., region 1330 in FIG. 13);

It should be appreciated that, in some embodiments, certain VSU I/O activity and compressibility level combinations above will only be considered as part of selecting a next VSU for certain system capacity utilization values or levels, for example, in accordance with compression decision rules described above in relation to FIG. 13 and Table 1.

As illustrated above, in some embodiments, methods 1400 and/or 1600 may be configured such that I/O activity level takes precedence (e.g., at least in most cases) over compressibility level in determining whether to compress a VSU, and in determining an order in which VSUs are considered for compression. In other embodiments, compressibility level may take precedence.

In some embodiments, for the compression order described above, for each I/O activity/compressibility level combination, VSUs are considered in order of longest time since compressibility value was last updated. That is, within each combinatory category, VSUs that have gone longer without being updated are accessed first. In some embodiments, other orders may be employed in which the time since compressibility was last updated takes precedence over I/O activity level and/or compressibility level. Other orders based on any combination of the above factors and/or other factors may be used as well. In embodiments in which the time since the compressibility value of a VSU was last updated is considered, field 1520 of the entry in data structure 1500 corresponding to the VSU may be accessed. Other data structures may be used.

In order to facilitate identifying a next VSU in act 1408, any of a plurality of data structures (e.g., indexes, ordered lists, linked lists) may be used, which list VSUs in accordance with one or more of the above orders. Such data structures may include one or more of the fields of data structure 1500 described above, and one or more entries in such data structures may include a link or reference to an entry (e.g., 1502-1508) of data structure 1500, e.g., using a VSU ID as a key.

If it is determined in act 1606 that there is not a next VSU to consider (e.g., based on compression decision rules), then method 1600 may be configured to return to act 1602 if running in continuous mode, or otherwise end if configured to run in response to some sort of event or input, as illustrated by arrow 1603. If it determined in act 1606 that there is a next VSU, then, in act 1608 it may be determined whether the system capacity utilization level is high. In some embodiments, if it determined to be high, the VSU data is compressed in act 1612, irrespective of the I/O activity level or compressibility level of the VSU.

If the system capacity utilization level is determined to not be high in act 1608, then, in act 1610, it may be determined whether to compress the VSU data based on the I/O activity level, compressibility level of the VSU and/or the system capacity utilization level according to compression decision rules, e.g., any of the variations described herein. Although not illustrated in FIG. 16, method 1600 also may be configured to determine whether to update a compressibility value and/or compressibility level for each VSU considered, e.g., after performance of act 1608, for example, as described above in relation to method 1400.

After a negative determination in Act 1610 or after performance of act 1612, method 1600 may return to act 1602. It should be appreciated that during the course of performance of method 1600, any of the following may change, for example, in response to performance of method 1400 or any other processes (e.g., FAST processes) running on the system: I/O activity level of one or more VSUs; the compressibility level of one or more VSUs; the system capacity utilization levels of the system or one or more system components; and factors and parameter values. Changes in on or more of these values may alter the decisions made as part of performing one or more acts of method 1600. Methods 1600 and 1400 may be considered dynamic in that their performances may adjust in response to changes in system parameter values—even during their execution.

It should be appreciated that method 1600 may include additional acts. Further, while the acts of method 1600 are illustrated in FIG. 16 as being performed serially, the invention is not so limited, and one or more of the acts, or parts thereof, may be performed concurrently, and two or more of the acts may performed in different orders than illustrated in or described in relation to FIG. 16. For example, the decisions of whether to compress VSU data and whether to update a compressibility value may be performed concurrently (at least in part).

Methods (e.g., methods 500, 1400 and/or 1600), and acts thereof, described herein, various embodiments and variations of these methods and these acts and other methodologies and techniques described above, individually or in combination, may be defined by computer-readable signals tangibly embodied on one or more computer-readable media, for example, non-volatile recording media, integrated circuit memory elements, or a combination thereof. Computer readable media can be any available media that can be accessed by a computer. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other semiconductor memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, other types of volatile and non-volatile memory, any other medium which can be used to store the desired information and which can accessed by a computer, and any suitable combination of the foregoing.

Communication media typically embodies computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, wireless media such as acoustic, RF, infrared and other wireless media, other types of communication media, and any suitable combination of the foregoing.

Computer-readable signals embodied on one or more computer-readable media may define instructions, for example, as part of one or more programs that, as a result of being executed by a computer, instruct the computer to perform one or more of the functions described herein, and/or various embodiments, variations and combinations thereof. Such instructions may be written in any of a plurality of programming languages or scripts, for example, Java, J#, Visual Basic, C, C#, or C++, Perl, Fortran, Pascal, Eiffel, Basic, COBOL, etc., or any of a variety of combinations thereof. The computer-readable media on which such instructions are embodied may reside on one or more of the components of any systems described herein, may be distributed across one or more of such components, and may be in transition there between.

The computer-readable media may be transportable such that the instructions stored thereon can be loaded onto any computer system resource to implement the aspects of the present invention discussed herein. In addition, it should be appreciated that the instructions stored on the computer-readable medium, described above, are not limited to instructions embodied as part of an application program running on a host computer. Rather, the instructions may be embodied as any type of computer code (e.g., software or microcode) that can be employed to program a processor to implement the above-discussed aspects of the present invention.

It should be appreciated that any single component or collection of multiple components of a system, for example, any of the systems described herein, that perform the functions described herein can be generically considered as one or more controllers that control such functions. The one or more controllers can be implemented in numerous ways, such as with dedicated hardware and/or firmware, using a processor that is programmed using microcode or software to perform the functions recited above or any suitable combination of the foregoing.

Having now described some illustrative embodiments of the invention, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other illustrative embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the invention. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. Acts, elements and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.

Use of an ordinal term such as “first”, “second”, “third”, etc., in the claims to qualify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as reference labels to distinguish one claim element (in a same or different claims) having a certain name from another element having a same name (but for use of the ordinal term). Use of an ordinal label other than “first” before a claim element does not mean that the invention recited in the claim necessarily includes at least one other element of the same name. For example, recitation of a “second” “item” in a claim does not mean that the invention recited in the claim necessarily includes a first “item.” Only recitation of a “first” “item” in the same claim or a claim from which the claim depends would necessarily make such element a part of the recited invention. 

What is claimed is:
 1. For a system comprising one or more physical data storage media and a plurality of virtual storage units, each virtual storage unit associated with one or more physical address ranges of the one or more physical storage media, a method comprising, for first data associated with a first of the plurality of virtual storage units, an act of: determining whether to compress the first data based at least in part on an I/O activity value of the first virtual storage unit; if it is determined to compress the first data, initiating compression of the first data; and determining whether to update a compressibility value in response to determining whether to compress the first data, wherein the compressibility value is associated with a compressibility level that is based upon an achievable compressibility value.
 2. The method of claim 1, wherein the act of determining whether to compress the first data is based at least in part on a compressibility value of the first virtual storage unit.
 3. The method of claim 1, further comprising an act of: determining whether to update a compressibility value of the first virtual storage unit; and if it is determined to update the compressibility value of the first virtual storage unit, updating the compressibility value.
 4. The method of claim 1, wherein the act of determining whether to compress the first data is based at least in part on a storage capacity utilization of the storage media or a subcomponent thereof.
 5. The method of claim 1, wherein the act of determining whether to compress the first data is performed in response to receiving a write I/O request for the first data.
 6. The method of claim 1, further comprising, prior to performing the act of determining whether to compress the first data, acts of: receiving an initial write I/O request for the first virtual storage unit, to write second data to a first one or more physical address ranges associated with the first virtual storage unit; and determining a compressibility value of the first virtual storage unit based on a compressibility of the second data, irrespective of a storage capacity utilization of the storage media or a subcomponent thereof.
 7. The method of claim 1, further comprising: determining that the compressibility value has not been determined for the first data for at least a threshold amount of time; and in response to determining that the compressibility value has not been determined for at least the threshold amount of time, determining a compressibility value for the first data.
 8. A system comprising: one or more physical data storage media and a plurality of virtual storage units, each virtual storage unit associated with one or more physical address ranges of the one or more physical storage media; first logic operative to, for first data associated with a first of the plurality of virtual storage units, determining whether to compress the first data based at least in part on an I/O activity value of the first virtual storage unit; second logic to initiate compression of the first data if it is determined to compress the first data; and fifth logic operative to determining whether to update a compressibility value in response to determining whether to compress the first data, wherein the compressibility value is associated with a compressibility level that is based upon an achievable compressibility value.
 9. The system of claim 8, wherein the first logic is operative to determine whether to compress the first data based at least in part on a compressibility value of the first virtual storage unit.
 10. The system of claim 8, further comprising: third logic to determine whether to update a compressibility value of the first virtual storage unit; and fourth logic to update the compressibility value of the first virtual storage unit if it is determined to update the compressibility value.
 11. The system of claim 8, wherein the first logic is operative to determine whether to compress the first data based at least in part on a storage capacity utilization of the storage media or a subcomponent thereof.
 12. The system of claim 8, wherein the first logic is operative to determine whether to compress the first data in response to receiving a write I/O request for the first data.
 13. The system of claim 8, wherein the first logic is operative, for an initial write I/O request for the first virtual storage unit specifying to write second data to a first one or more physical address ranges associated with the first virtual storage unit, to determine a compressibility value of the first virtual storage unit based on a compressibility of the second data, irrespective of a storage capacity utilization of the storage media or a subcomponent thereof.
 14. The system of claim 8, further comprising: third logic to determine that the compressibility value has not been determined for the first data for at least a threshold amount of time; and fourth logic to determine the compressibility value for the first data in response to determining that the compressibility value has not been determined for at least the threshold amount of time.
 15. A non-transitory computer-readable medium encoded with computer-executable instructions that, as a result of being executed by a computer, control the computer to perform, for a system comprising one or more physical data storage media and a plurality of virtual storage units, each virtual storage unit associated with one or more physical address ranges of the one or more physical storage media, a method comprising, for first data associated with a first of the plurality of virtual storage units, an act of: determining whether to compress the first data based at least in part on an I/O activity value of the first virtual storage unit; if it is determined to compress the first data, initiating compression of the first data; and determining whether to update a compressibility value in response to determining whether to compress the first data, wherein the compressibility value is associated with a compressibility level that is based upon an achievable compressibility value.
 16. The computer-readable medium of claim 15, wherein the act of determining whether to compress the first data is based at least in part on a compressibility value of the first virtual storage unit.
 17. The computer-readable medium of claim 15, wherein the method further comprises an act of: determining whether to update a compressibility value of the first virtual storage unit; and if it is determined to update the compressibility value of the first virtual storage unit, updating the compressibility value.
 18. The computer-readable medium of claim 15, wherein the act of determining whether to compress the first data is based at least in part on a storage capacity utilization of the storage media or a subcomponent thereof.
 19. The computer-readable medium of claim 15, wherein the act of determining whether to compress the first data is performed in response to receiving a write I/O request for the first data.
 20. The computer-readable medium of claim 15, wherein the method further comprises, prior to performing the act of determining whether to compress the first data, acts of: receiving an initial write I/O request for the first virtual storage unit, to write second data to a first one or more physical address ranges associated with the first virtual storage unit; and determining a compressibility value of the first virtual storage unit based on a compressibility of the second data, irrespective of a storage capacity utilization of the storage media or a subcomponent thereof. 